Administrative details

CISC 105 – Topic 1 1

Administrative details Project #1 due Tuesday Lab #6 on Tuesday Midterm exam next week Content for exam:

General computer knowledge Unix commands C language Chapters 1-5 Afzal Chapters 1-4 Deitel Class slides Lab work Homework

Topic 1: Introduction to Computers and Programming

“A journey of a thousand miles must begin with a single step.” - Lao Tzu


Binary MathA binary digit or bit for short is the smallest unit of

computer information. Just as our familiar decimal number system has 10 digits,(0,1,2,3,4,5,6,7,8,9) the binary number system has only 2 digits (0,1). This is the perfect number system for computers since we can store a binary digit by making an electrical or magnetic field either on or off, positive or negative, 1 or 0. In the decimal system we can count 10 (we start counting with 0) items with one decimal place, 100 with two decimal places, 1000 with three decimal places and so on.


Binary MathThe binary number system works the same way

except since we only have 0s and1s our base is 2.

So we can count 2 permutations of 1 bit: 0 14 permutations of 2 bits: 00 01 10 118 permutations of 3 bits: 000 001 010 011 100 101

110 11116 permutations of 4 bits: 0000 0001 0010 0011

0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111

...and so on.


Binary MathSo in an eight bit byte, the numbers are represented this

way:

Bit: - - - - - - - -Value: 128 64 32 16 8 4 2 1

Example: 1 0 1 1 0 1 1 0

Values: 128 + 0 + 32 +16 + 0 + 4 + 2 + 0 = 182

The minimum number is 0 (all 0s) and the maximum number is 255 (all 1s), so you can represent 256 numbers (0-255) with one byte.


Hardware Components Hardware consists of many types

of components: Primary Storage Secondary Storage The Central Processing Unit (CPU) Input Devices Output Devices


Primary Storage andSecondary Storage There are two primary types of

storage in a computer: Primary Storage – often referred to as

main memory, or just memory. This storage is very quickly accessed by the various hardware components.

Secondary Storage – includes such devices as a hard disk, floppy disk, CD-ROM, DVD-ROM, etc…


Computer Software All major computers run an

operating system. An operating system is a special

type of program which controls the interaction between all hardware components and the user.


Operating Systems Tasks Responsibilities of the OS include:

Communicating with the user(s) Managing resources including memory

and processor time among programs Collecting data from input devices Providing data to output devices Accessing data from secondary storage Writing data to secondary storage


Computer Programming - Machine Language Computer programs were originally written

in machine language. Machine language is a sequence of binary numbers, each number being an instruction.

Each instruction is computer-understandable.

000000000001010100010110


Computer Programming - Assembly Language To make machine language more abstract,

assembly language was introduced. Assembly language provides a one-to-one

mapping between a machine instruction and a simple human-readable instruction.

Assembly language is converted to computer-understandable machine language by an assembler.

000000000001010100010110

CLR AADD AADD B


Computer Programming – High-Level Languages In order to get around these obstacles, high-

level languages were introduced. High-level languages provide a one-to-many

mapping between one high-level statement and multiple assembly language instructions.

High-level language is converted to assembly instructions by a compiler, which creates object files. Modern compilers perform the assembler function as well.


Modern Software Development Programmers often use library functions,

which are pre-written functions provided as part of the compiler/development toolset.

A library is an object file. After the source code is compiled into

machine code, a linker resolves cross-references among these object files, including libraries. The object files are linked into an executable file.


Modern Software Development

Source Code File Compiler

Object File

Executable FileOther Object Files(perhaps libraries) Linker

Loader


The Software Development Method Specify the problem. Analyze the problem. Design an algorithm to solve the

problem. Implement the algorithm. Test and verify the program. Maintain and update the program.


Review Name the principle components of a

computer.

What advantages does assembly language have over machine language?

What are three responsibilities of the operating system?

What advantages do high-level languages have over assembly language?


Review What computer program translates a

source code file into an object file? What program combines object files and

produces an executable file? What part of the operating system is

responsible for the loading and scheduling of programs?

What are the steps in the software development method?

Topic 2 – Introduction to the C Programming Language


Preprocessor Directives A preprocessor directive is a command

given to the C preprocessor, which is a part of the compilation process that modifies a C source code file before it is compiled.

Preprocessor directives always begin with a “#” character.

In the example program, there are two preprocessor directives used, #include and #define.


#include The #include directive tells the C

preprocessor to give a program access to a library. By putting a #include in a program, the preprocessor loads a header file, which tells the compiler what functions and other information is provided in the library.

In this program, #include <stdio.h> indicates that this program uses the stdio library which contains functions such as printf(). Page 542 of Deitel lists standard libraries.


#define The #define directive specifies a

constant macro. This tells the preprocessor that every

time it encounters the first text, it should replace it with the second text.

In this program, #define KMS_PER_MILE 1.609 tells the preprocessor to replace KMS_PER_MILE with 1.609 every place KMS_PER_MILE appears in the program.


Preprocessor Directives/* Converts distances from miles to kilometers */

#include <stdio.h>#define KMS_PER_MILE 1.609

int main(void){

double miles, /* distance in miles */kms; /* equiv. distance in kms */

/* Get the distance in miles */printf(“Enter the distance in miles>”);scanf (“%lf”, &miles);

/* Convert the distance to kilometers */kms = KMS_PER_MILE * miles;

/* Display the distance in kilometers */printf (“That equals %f kilometers.\n”,kms);

return(0);}




int main(void){





return(0);}

#include directive –Tells the preprocessor to include the stdio.h header file.This file describes the functionsand other information included in the stdio library.




int main(void){





return(0);}

#include directive –Tells the preprocessor to include the stdio.h header file.This file describes the functionsand other information included in the stdio library.

#define directive –Tells the preprocessor to replace every occurrence ofKMS_PER_MILE in the programwith 1.609.


What is a valid identifier? Identifiers can only be composed of

letters, digits, and underscores. Identifiers cannot begin with a digit. Reserved words cannot be identifiers. Identifiers can be as long as you

want. Upper and lower case letters are

different (i.e. kms and Kms are not considered to be the same identifier).


Review Which of the following are valid identifiers? For

each that is not valid, why is it not?

This_is_a_long_identifier_but_is_it_valid?8timesTheRadiusmilesPhil’s variablekilometers_per_hour

“radius”x


Variables A variable is a memory cell that is used

to hold data acted upon by the program. A variable declaration tells the C

compiler the name and type of a variable used in a program.

A variable declaration consists of a data type and an identifier which is the name of that variable.

Every variable that will be used in a program must be declared.


Variable Declarations

The first line declares a variable named mile of the double data type.

The second line declares a variable named counter of the int data type.

double mile;int counter;


Data Types There are a large number of data types.

These are some of the most popular ones.

void – this keyword means “no data type”.

int – An integer (a whole number). This data type can represent an integer in a specific range, at least –32767 through 32767.


Data Types char – A character. One letter, digit, or

symbol. This is enclosed in single quotes. float – A real number (an integer part and

a decimal part). double – A real number. Note that this data

type is a memory cell double the size of a float data type. This allows a bigger number to be represented, or a specific number to be represented more precisely. This is referred to as a double-precision floating point number.


Review of Variables Write a #define preprocessor declaration for a

constant macro of STUDENTS_PER_SECTION to 22 and variable declarations of num_students as an integer, GPA and class_GPA as double-precision floating point numbers, and letter_grade as a character data type.

#define STUDENTS_PER_SECTION 22

int num_students;double GPA, class_GPA;char letter_grade;


Assignment Statements An assignment statement is one

type of executable statement. An assignment statement uses the

“=“ operator, and follows the form:variable = expression;

This statement first evaluates the expression on the right and stores the result in the variable on the left.


Assignment Statements Here are some examples of assignment

statements: x = 12; negative_x = -x; x = y + 12 + z * 5; result = y;

Note that any variables in the right-side expression are not modified by an assignment statement.


Function Calls A function is a piece of code which

performs a specific task. Functions can be created by programmers

or supplied as part of the C compiler toolset.

A function is called, which causes it to execute.

A function call is composed of the function name, an open paren, a set of function arguments separated by commas, and a close paren.


Function Calls A function call looks like this:

function_name(argument1, argument2, argument3);

function name function arguments

open paren close paren


The printf Function The C function for displaying output on

the screen to the user is printf. printf is called in the following manner:

printf(“The final GPA of student number %d is %f.\n”,student_num, GPA);

format string print list

function arguments


The Format Stringand Print List The format string is the text that is to

be displayed on the screen. The “%” characters are called

placeholders. They indicate the display position for variables whose values are to be displayed.

The variable names to be displayed are specified in the print list and appear in the same order as their placeholders.


Placeholders


This pair specifies the location in the printstring to display the student_num value.

This pair specifies the location in the printstring to display the GPA value.


Placeholders All placeholders begin with a “%”. The text after the “%” symbol

indicates how to format the output, i.e. what kind of variable it is. %d – decimal number (int) %f – floating-point number (float or double)

%c – character (char)


Escape Sequences All escape-sequences begin with a

backslash, “\”. A letter after the “\” character denotes

an escape sequence, which has special meaning.

The “\n” sequence indicates a new-line character, which cause any following text to appear on the next line on the display.

In order to display a “\”, the format string must contain a “\\”.


Placeholders and theNewline Escape Sequence


Specifies to display student_num,which is an integer.

Specifies to display GPA,which is an floating-point number.


Placeholders and theNewline Escape Sequence


Specifies to display student_num,which is an integer.

Specifies to display GPA,which is an floating-point number.

Therefore, if the student_num variable was set to10 and the GPA variable was set to 3.03

this printf function call would cause:

The final GPA of student number 10 is 3.03.

to be displayed on the screen and any subsequent output to begin on the next line.


The scanf Function The C function for reading input

from the user is scanf.

scanf(“%d %f”,&student_num, &GPA);

format stringinput list

function arguments


The Format String The format string is the set of

placeholders which specify what type of data is being input.

The same placeholders are used as for printf, except for when inputting a floating-point number. A float type still uses the “%f”, however the double type uses the “%lf” placeholder.


The Input List The variables to store the inputted data are

specified in the input list. They must be in the same order as their corresponding placeholders.

Notice that each variable name is preceded by a “&”.

The “&” is an operator which means “the address of”.

Therefore, “&student_num” tells the scanf function to store what it reads from the user at the memory address of student_num.


Placeholders and the Input List


This pair specifies to readin an integer and store itat the memory address ofstudent_num, thus settingthe student_num variable

to the inputted value.




This pair specifies to readin a single-precision floating

point number and store itat the memory address ofGPA, thus setting the GPA

variable to the inputted value.




Therefore, if the input into thisscanf function call was:

9 3.560 <ENTER>the student_num variable would be

set to 9 and the GPA variable would beset to 3.560


Review of printf and scanf What is the displayed output when

the following code fragment is run and the inputs are 8 and 12?

int x, y;

printf(“My name is”);printf(“ Phil Viscito”);printf(“\nEnter two integers> ”);scanf(“%d%d”,&x, &y);x = x + 2;y = x + y;printf(“Thanks! The answer is %d.\nBye now!”,y);

My name is Phil Viscito.Enter two integers> 8 12Thanks! The answer is 22.Bye now!


Customizing Integer Output The “%d” placeholder, used to display an

integer variable, can be altered to format how the number is displayed.

Instead of “%d”, use a “%Xd” where the X is an integer that is the field width, the number of digits to display.

For example, “%4d” displays four digits of the result. The negative sign (for negative integers) is also considered a digit here.


Customizing Integer Output When there are more places (the

field width) than digits to be displayed, the output is right-justified.

When there are more digits than places, the field width is ignored, and the entire integer is displayed.


Customizing Integer Output As an example:

Value Placeholder Output

643 %1d 643

643 %4d 643

643 %5d 643

-643 %2d -643

-643 %6d -643


Customizing Floating-Point Output Floating point output (float and double)

can be formatted in the same manner, using “%X.Yf”).

Here, X is the total number of digits to display (the field width) and Y is the number of digits to display to the right of the decimal point.

The same rules for field width apply as for integer formatting.

The specified number of decimal digits is always displayed.


CustomizingFloating-Point Output

Value Placeholder Output

3.14159 %5.2f 3.14

3.14159 %3.2f 3.14

3.14159 %5.3f 3.142

0.1234 %4.2f 0.12

-0.006 %8.5f -0.00600

As an example:


Arithmetic Expressions Arithmetic expressions are executable

statements that manipulate data. Arithmetic expressions operate on both

integer (int) and floating-point (float and double) numbers.

Arithmetic operators can operate on mixed types (i.e. one int and one float). The resulting type of such an expression is the “highest” data type present.


Resulting Data Types The “highest” data type is always

considered to be a floating point number, with double-precision floating point numbers taking precedence over single-precision floating point numbers.

int + int = intint + float = floatint + double = doublefloat + double = double


Arithmetic Expressions All of the common arithmetic

operators are present in C: + (addition) - (subtraction) * (multiplication) / (division) % (modulus – or “remainder”)


Note: Integer Division If two integer values are divided,

the resulting data type is also an integer, as previously described.

Therefore, only the integer portion of the actual result will be the returned result.

For example, 9 / 4 = 29 / 10 = 0


The Modulus Operator The “%” operator is a modulus

operator, which also means the remainder of the division.

For example,

9 % 3 = 010 % 6 = 490 % 8 = 2


Review of BasicArithmetic Expressions What is the resulting output of this

program segment?

int x, y, z;float a;

x = 9 * 0.5;a = 9 * 0.5;y = 15 % 15;z = 15 % 2;printf(“x=%d\n, a=%f\n, y=%d\n, z=%d\n”,x,a,y,z)

x=4a=4.5y=0z=1


More ComplexArithmetic Expressions C evaluates arithmetic expressions

in the same order rules as normal mathematics. Parentheses take priority over

everything else. Then, multiplication, division, and

modulus operations from left to right. Then, addition and subtraction from

left to right.


More ComplexArithmetic Expressions

x2 + 2xy + 4y2 (x * x) + (2 * x * y) + (4 * y * y)

a + b--------c2 * 4d

(a + b) / (c * c * 4 * d)

a * (4x % y2) a * (4 * x % (y * y))

x + y(x2 + y) x + y * (x * x + y)


Review

#definePI 3.14159

int x, y, z;float a, b;

x = 5;y = 10;z = x + (4 * y * y * y) + PI;a = x + (4 * y * y * y) + PI;b = (x / y) + a;

printf(“x=%d, y=%d, z=%d\na=%7.2f, b=%f\n”,x,y,z,a,b);

What is the resulting output of this program segment?

x=5, y=10, z=4008a=4008.14, b=4008.14159

Since x and y are both integers, this evaluates to 0!


Another Special Case:Increment and Decrement Incrementing (adding one) and

decrementing (subtracting one) are two very common operations.

C has a special syntax for increment and decrement operations that follows this form:x++; ++x; --x;x--;OR OR

Increment Decrement


Another Special Case:Increment and Decrement

Notice that the increment operator expression x++ is the same as saying: x += 1;

So, why are there two forms of each operator? The answer lies in when the increment (or

decrement) operation is actually performed. This distinction only occurs when the ++ (or --)

operator is used on a variable in the same expression in which the value of the variable is used.


Another Special Case:Increment and Decrement For example,

int x = 20, y;

y = x++;printf(“x=%d, y=%d\n”,x,y);

int x = 20, y;

y = ++x;printf(“x=%d, y=%d\n”,x,y);

x=21, y=20 x=21, y=21

y = x;x += 1;printf(“x=%d, y=%d\n”,x,y);

x += 1;y = x;printf(“x=%d, y=%d\n”,x,y);


Another Special Case:Increment and Decrement The difference lies in when the expression

(x++ or ++x) gets evaluated in relation to when the operator (++) gets performed.

The x++ expression is equal to the value of x and the ++ operator is performed after the evaluation is over.

The ++x expression indicates that the ++ operator is performed first (before ++x is evaluated) and thus, is equal to the value of x + 1.


Review What is the output of the following

program fragment?

int x, y, z;

x = 5;y = 10;

z = x++ * y – 2;z += ++x;

printf(“x=%d, y=%d, z=%d\n”,x,y,z);

x=7, y=10, z=55

Topic 2A – Library Functions and Casting


Casting Although each of the functions above

take (and return) double data types, they can be used with float data types.

This is done with a cast. A cast is the conversion of one data

type to another data type. This can be done explicitly or implicitly.


Implicit Casting When evaluating mixed type expressions,

an implicit cast is performed, as mixed type expression cannot be directly evaluated.

For instance, in the code fragment:float x = 1.0, y;int z = 2;

y = x + z;

The variable z is casted to a float (2.0) in order to add it to the float-type x.


Review What is the result of the following

code fragment:int w, z, q;float x = 4.0, y;

y = sqrt(x);w = y;z = x – w;q = sqrt(3);

printf(“y=%f,w=%d,z=%d,q=%d”,y,w,z,q);

y=2.0, w=2, z=2, q=1


Explicit Casting Casting can also be performed

explicitly. This is done with the following form. What is the result of the following code fragment?

int a=9, b=4;float c,d;

c = a/b;d = (float)a / (float)b;

printf(“c=%.2f,d=%.2f”,c,d);

c=2.00, d=2.25

Topic 3 – The General Form

of a C Program


The main Function Header Thus, a general C program looks like:

Preprocessor directives

int main(){

variable declarations

executable statements

return(0);}


Review (Problem #1) Write a complete C program that

asks the user for a floating-point number, multiplies the number by 4 * PI (with PI set to 3.14159 in a constant macro) and then outputs the result.


Review (Problem #1) Write a complete C program that

asks the user for a floating-point number, multiplies the number by 4 * PI (with PI set to 3.14159 in a constant macro) and then outputs the result.

#include <stdio.h>#define PI 3.14159

int main(){

float number, answer;

printf(“Number?”);scanf(“%f”,&number);answer = number * 4 * PI;printf(“The answer is:%f\n”,answer);return (0);

}

Topic 5 – Control Structures


The if statement In order to use a condition to make a

decision about program control flow, C uses an if statement.

The if statement first evaluates the specified condition.

If the condition is true, the statement immediately following the if statement executes. If the condition is false, the statement immediately following the if statement is skipped.


The if/else Statement In addition, C supports the use of an else

statement. This statement can follow the optional

statement (the one that may or may not execute depending on the condition).

If there is an else statement, the statement immediately following the else statement will execute if the original condition (in the if statement) is false.


The if/else Statement Therefore, if there is an else

statement, either the statement immediately following the if statement is run (if the condition is true) OR the statement immediately following the else statement is run (if the condition is false).


The if/else Statementstatement1;if (condition)

statement2;else

statement3;statement4;

In this program fragment, statement1 executes. Then, either statement2 or statement3 executes, depending on the condition. Then, statement4 executes. Note that only 3 statements execute.


Compound Statements Sometimes, we wish to perform more than

one thing as the result of an if statement. In this case, we can make use of a

compound statement. A compound statement is a group of C

language statements that run sequentially. A compound statement is enclosed with curly braces (“{” and “}”), in the same way a function body is.


Compound Statements When used as the statement

immediately following an if or else statement, a compound statement is treated like one statement (all of the statements enclosed by the braces are run, sequentially.)


Compound Statements

statement1;if (condition){

statement2;

statement3;}else{

statement4;

statement5;}statement6;

In this program fragment, statement1 executes. Then, either statement2 and statement3 execute or statement4 and statement5 execute, depending on the condition. Then, statement6 executes. Note that only 4 statements execute.


Cascading if/else Statements

statement1;if (condition1){


}else if(condition2){


}else


We can also cascade if/else statements. Here, condition1 is first evaluated. If it is true, statements 2 & 3 run and then statement7. If condition1 is false and condition2 is true, statements 4 and 5 run and then statement 7. If both conditions are false, statement 6 runs and then statement 7.

Note that if condition1 is true, condition2 is never evaluated!


Conditions So, now the structure of if/else

statements are known. So, how do we write the conditions?

When an if statement is encountered, the program will first evaluate the condition in the if statement. Anything that evaluates to a nonzero value is true. Anything that evaluates to zero is false.


Conditions Thus, an if statement that was

written as:

would cause statement1 to run if x wasequal to any value other than zero. Ifx was zero, statement1 would beskipped.

if (x)statement1;


Relational and Equality Operators In order to write conditions

effectively, C provides a number of relational and equality operators.

For these operators, if the condition they specify is true, they evaluate to 1. If the condition they specify is false, they evaluate to 0.


Operators The following relational and

equality operators are used: < less than > greater than <= less than or equal to >= greater than or equal to == equal to != not equal to


Conditions & Operators Some examples of the use of these

operators include: x <= 0 number > MAX_NUMBER_ALLOWED male_or_female == ‘M’ num != flag_number y < 12.0 q <= p


A VERY Common Error An assignment statement evaluates to the

value being assigned. For example,

x = 6;

evaluates to 6. So…what would happenif we wrote

if (x = 6){

…}


A VERY Common Error An assignment statement evaluates to the

value being assigned. For example,

x = 6;

evaluates to 6. So…what would happenif we wrote

if (x = 6){

…}

First, 6 would be assigned to x!This overwrites whatever was previously

stored in x. Also, x=6 evaluates to 6.As anything nonzero is true, this condition

is ALWAYS true.

BOTTOM LINE:

Remember to use == for conditions!


Compound Conditions More than one condition can be

combined to create a compound condition.

A logical operator is used to combine conditions. These include: && AND || OR (shift-\)


Logical AND (&&) The logical AND operator works as

follows:Condition 1 Condition 2 Overall Result

TRUE (nonzero)

TRUE (nonzero)

TRUE (1)

TRUE (nonzero)

FALSE (0) FALSE (0)

FALSE (0) TRUE (nonzero)

FALSE (0)

FALSE (0) FALSE (0) FALSE (0)


Logical OR (||) The logical OR operator works as

follows:Condition 1 Condition 2 Overall Result

TRUE (nonzero)

TRUE (nonzero)

TRUE (1)

TRUE (nonzero)

FALSE (0) TRUE (1)

FALSE (0) TRUE (nonzero)

TRUE (1)

FALSE (0) FALSE (0) FALSE (0)


Logical NOT (!) The last logical operator is the NOT

operator. It behaves as follows:

Condition !(Condition)

TRUE (nonzero) FALSE (0)

FALSE (0) TRUE (1)


Examples Write a condition that is true if both x is

greater than 19.75 and number is equal to 3 OR big_letter is not equal to ‘Q’.

(X > 19.75 && number == 3) || big_letter != ‘Q’


The switch Statement When one variable (type int or char

ONLY) is used to make a control decision, where different statements are run if the variable is equal to different values, the switch statement can be used.

Note that this statement does not allow less than, greater than, etc. ONLY the equality operator (==) is used with a switch statement.

The switch statement is composed of a control variable and a series of case clauses.


The switch Statement

The switch statement takes this form:

switch(control variable){

case (value1):. . .. . .break;


default:. . .. . .break;

}


The switch Statement When the switch

statement is encountered, the control variable is evaluated. Then, if that evaluated value is equal to any of the values specified in a case clause, the statements immediately following the colon (“:”) begin to run.





}



These statements then continue to run until a break statement is encountered. Control then flows to the statement immediately following the closing brace (“}”).





}



It is important to remember that control will pass into the next case clause if a break statement is not encountered.





}



So, what happens if the control variable is not equal to any of the values specified in the case clauses?

The default case clause runs.





}


switch Statement Examplestatement1;switch(x){

case (3):statement2;statement3;case (27):case (1):statement4;case (2):statement5;break;default:statement6:statement7:break;

}statement8;

Which statements run if:

x = 1?x = 2?x = 3?x = 10?x = 27?

Topic 6 – Repetition and Loops


The while Statement In order to create loops in the C

language, the while statement can be used. This statement follows the form:

while (condition){

statement1;statement2;. . .

}


The while Statement When the while statement

is first encountered, the condition is evaluated. If it is true (nonzero), the loop body executes sequentially. If the condition is false, the loop body is skipped. Notice that this behavior is exactly the same as a simple if statement.

while (condition){


}


The while Statement At the end of the loop body

(when the closing brace “}” is encountered) the condition is evaluated again. If it is true, the loop body begins to execute again, beginning with the first statement in the body (immediately following the open brace “{”) and continuing to the end sequentially.

while (condition){


}


Counting Loops and while Statements As we have seen, counting loops have

three principle components when created with a while statement: Initialization – set the initial value of

the loop control variable (usually to zero) Testing – Test the value of the loop

control variable according to the condition

Updating – Update the loop control variable as the last statement in the loop


A Common Loop Error What happens if, when writing a

counting loop, the programmer does not update the loop control variable?

The condition will always be true(assuming it starts off as true). Thus,the loop with execute forever. This

is referred to as an infinite loop.


The for Statement As we have seen, many loops have

three components in addition to the loop body: Initialization – set the initial value of

the loop control variable Testing – Test the value of the loop

control variable according to the condition

Updating – Update the loop control variable


The for Statement The for statement offers a designed

place for each of these three components. It follows the form:

for (counter = 0; counter < high_value; counter++){


}


The for Statement Thus, the for

statement consists of an initialization, a semicolon, the condition, a semicolon, and the an update statement.



}


The for Statement Notice that the

update statement does NOT have a semicolon.

Also, the initialization and update statements can actually be composed of more than one statement.



}


The for Statement If more than one

statement is to be used for initialization or update, these statements are separated by commas.

for (counter = 0, x = 0; counter < high_value; counter++, x += 2){


}


for / while Loop Equivalence Notice that any for loop can be

rewritten into a while loop. The for loop is simply a special

case of the while loop, with provisions for initialization and updating build into the loop statement itself.


for / while Loop Equivalence To convert from a for loop to a

while loop, simply move the initialization statement(s) before the loop statement and move the update statement(s) inside the loop body.

We can rewrite the payroll example using a for loop instead of a while loop.


The Payroll Examplewith a for Loop

printf(“How many employees do you have?”);scanf(“%d”,&number_employees);total_pay = 0.0;for (counter = 0; counter < number_employees; counter++){

printf(“Hours?”);scanf(“%d”,&hours);printf(“Pay rate?”);scanf(“%lf”,&rate);pay = hours * rate;printf(“The pay is %f.\n”,pay);total_pay += pay;

}printf(“Total pay = %f.\n”,total_pay);


The do-while Statement Both of the loop statements we have seen

evaluate the condition before the first loop iteration.

Sometimes, we wish to check the condition at the end of the loop iteration, instead of at the beginning of the loop iteration.

This has the effect of ALWAYS executing the loop the first time, then testing the condition at the end of the loop iteration.


The do-while Statement In order to create such loops, C

offers the do-while statement. This loop follows the format:

do{


} while (condition);


The do-while Statement When the do

statement is first encountered, the loop body begins to execute immediately.

When the loop body completes, the while statement is reached.

The condition is then evaluated.

statement1;do{


} while (condition);statement4;


The do-while Statement

Notice that the while statement has a semicolon at the end of the condition.

statement1;do{




The do-while Statement So…the do-while loop

statement is the same as the while statement except the condition is tested at the end of the loop iteration rather than the beginning.

Thus, a do-while loop ALWAYS executes at least once.

statement1;do{




do-while and while Comparison Do the following loops do the same thing?

scanf(“%d”, &num);while (num != SENTINEL){

/* do something with num */scanf(“%d”, &num);

}

do {scanf(“%d”, &num);if (num != SENTINEL){

/* do something with num */

}} while (num != SENTINEL)

Loop #1 Loop #2Yes, the loops do the same thing.Is one better than the other? Why?


Common Loop Errors Find the error(s) in the following code:

#include <stdio.h>

/* This program asks for a number and displays that many lines of stars on the screen. */

int main(){

int count, num_lines;printf (“How many lines would you like?”);scanf(“%d”,&num_lines);for (count = 0; count <= num_lines; count++)

printf (“********************\n”);return 0;

}


Common Loop Errors Find the error(s) in the following code:

#include <stdio.h>/* This program asks for numbers and keeps a running sum. It terminates when –99 is entered. */int main(){

int sum, number;do {

printf(“Enter a number (-99 to quit)>”);scanf(“%d”,&number);sum += number;

} while (number != -99);printf (“The sum is %d.\n”,sum);return 0;

}

Date post:	02-Jan-2016
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