Chapter 3 Flow Control

By C. Shing

ITEC Dept

Radford University

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Objectives Understand how to use assignment statement Understand how to use conditional statement Understand how to use loop statement

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Assignment Statement Identifier assignment_operator expression;Represents

identifier = identifier assignment_operator(expression);

After evaluating the right hand side of =, it stores result to the left hand side identifier

(i.e. memory) and change to the data type of left hand side

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Assignment Statement – assignment operator

Assignment operator =, +=,-=, *=, /=, %=

Example:

x *= 3

Means x=x*3

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Assignment Statement (Cont.) Identifier = expression;

Both sides of data type should match. If not, then

the right hand side of type will be widened

automatically to the left hand side data type.

Otherwise, warning message will be given

for narrowing data type.

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Assignment Statement (Cont.) Type conversion:

Automatic conversion rule Manual conversion: use casting

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Assignment Statement (Cont.) Automatic conversion rule:

The widest data type in an expression determines the

data type of the expression unsigned type is wider than the corresponding

type the rest from widest: double, float, long, int, short (or char)

Finally, the expression data type will be widened to

the data type of the identifier

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Assignment Statement (Cont.) Examples:

unsigned u;

long g;

int i;

unsigned long ul;

ul = u-3*g +i; // right hand side result type

// long is converted to unsigned long

// before stored in ul

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Assignment Statement (Cont.) Examples:

unsigned u;

float f;

int i;

double db;

db = u/3-i+f; // right hand side result type

// float is converted to double before

// stored to db

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Assignment Statement (Cont.) Casting:

Identifier = (left hand side type) (expression)

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Assignment Statement (Cont.) Examples:

unsigned u;

long g;

int i;

unsigned long ul;

i = (int) (u-3*g +4); // right hand side result type

// is long

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Conditional Statement - if if, if .. else, ?:, switch if form:

if (condition)

{

…

}

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Conditional Statement – if (Cont.)Note: condition is evaluated using short-circuitIf condition consists of condition1 and condition2 connected by a logic operator:

Condition1 && condition2 if condition1 is false,

then it will not evaluate condition2 Condition1 || condition2 if condition1 is true,

then it will not evaluate condition2

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Conditional Statement – if (Cont.) Example:

int x; if (x = 5)

{

printf(“Always TRUE is printed!\n”);

}

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Conditional Statement – if … else if … else form:

if (condition) {

… } else {

… }

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Conditional Statement – if … else (Cont.)

Example: if (x<y) {

min = x; } else {

min = y; }

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Conditional Statement – ?: form: identifier =

(condition)?true part:false part

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Conditional Statement – ?: (Cont.) Example: (Same example as previous one)

min = (x<y) ? x : y;

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Conditional Statement – switch switch form: values (char/int) cannot be range as in

Visual Basic switch (expression)

{

case value1:

…

break; // quit the current (switch) statement

case value2:

case value3:

…

break; // do this part when value2 or value3

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Conditional Statement – switch (Cont.)

switch form: (Cont.) case …:

…

break;

default: // everything else

…

}

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Conditional Statement – switch (Cont.) Example:

switch (character) { case ‘a’: case ‘A’: a_count++;

break;…default:

printf(“%c is not a letter!\n”, character);}

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Loop Statement while do … while forSteps of writing a loop:1. Identify the loop body: repetition part2. Identify condition that can make the repetition of loop body either true of false;Make sure the first time, condition is true3. Initialize loop condition before loop4. Update loop condition at end of loop body

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Loop Statement - while while form: repeat loop body when condition is

true – pre-condition while (condition part)

{

…

}Note: condition part can be more than one statement,

separated by a comma

Example: while (scanf("%c", &character), character !='\n');

What task does the statement above perform?

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Loop Statement - while Condition can be

Counter control (definite loop): use counter

Example:int count=1; // the following prints out 5 times onlywhile (count <= 5)

{ ++count;

printf(“%d\n”, count);}

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Loop Statement - while Condition can be (Cont.)

Sentinel control (indefinite loop): use pseudo data (sentinel) for condition

Example: sentinel data is any negative scoreint score;scanf(“%d”, &score);while (score >= 0)

{ printf(“%d\n”, score);

scanf(“%d”, &score);}

Yard-Meter Conversion

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Loop Statement - while Condition can be (Cont.)

More than 1 statement

Example:

Skip 1st Line

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Loop Statement – while (Cont.) Example:

Hard –to-find Error:

int x;

// the following is an infinite loopwhile (x = 5)

{

printf(“Always TRUE is printed!\n”);

}

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Loop Statement – while (Cont.) Example: (Use break to get out of loop) int x, count=0; // the following prints out TRUE 5 times only

while (x = 5) { ++count;

printf(“Always TRUE is printed!\n”); if (count == 5) break; }

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Loop Statement – do while do while form: repeat loop body when condition

is true – post-condition do

{

…

} while (condition);

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Loop Statement – do while (Cont.) Example:

int x=0;

do {

++x;

printf(“Always TRUE is printed!\n”);

} while (x != 5)

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Loop Statement - for for form: repeat loop body when condition is

true – pre-condition Most general form: can represent

while and do while loops

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Loop Statement – for (Cont.) for (initialization, exprPart1, …;

exprPart2, …,condition;

exprPart3, …,last statement in loop body) {

…

}

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Loop Statement – for (Cont.) Example:

int i; // loop index must be defined

// outside for loopfor (i=0;i<5;++i)

{

printf(“TRUE is printed!\n”); // print 5 times

}

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Loop Statement – for (Cont.) Example: (Same as the previous one)

int i=0;

// print 5 timesfor (;i<5; printf(“TRUE is printed!\n”), ++i);

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Loop Statement – for (Cont.) Example: (Use continue statement to skip current loop) int x, count=0; // the following prints out TRUE 5 times only

while (count <=10) { ++count; if (count %2 == 1) // skip odd number times of print continue;

printf(“TRUE is printed!\n”);}

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Loop Statement – for (Cont.) Represent while loop:

for (;condition;) {

…

}

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Loop Statement – for (Cont.) How to check end of file:1. If read a character: (Must deal with \n)Use scanf(“%c”, &c)>0 to read in a character to check any character being read (if reach to end of file, scanf returns -1)

Example 1: a.out < checkEOF.c

2. If read an integer:Use scanf(“%d”, &number)>0 to read

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Loop Statement – for (Cont.) Represent do while loop:

for (;loop body statements, condition;);

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Keyboard Input Format Function - scanf Form: scanf(“pure_format”, variable_address);

Format: similar to those used in printf, however, no character or strings included

%i: for decimal, octal (data begins with 0) or hexadecimal (data begins with 0x) If use %s format, it reads all until it reaches the first white space &variable represents the address of the memory (or variable)

Example:char c;int i;double db;char s[80]; // remember s is address: array of 80 charactersscanf(“%c%d%lf%s”, &c, &i, &db, s); // sample data:a 100 -1.23 This is a sample data// c=‘a’, i=100, db=-1.23, s=“This”

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Class Example Example 1 Example 2 : print character ‘2’

in front of each line Read Character : read a character after reading a

number For loop

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Assignment Assignment #1

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Practice

Given int a=1,b=2,c=3,d=4;

Find the values of the following table:

Expression Value

________ _____ a +=b+c a=

b *=c=d+5 b=

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Practice - Answer

Given int a=1,b=2,c=3,d=4;

Find the values of the following table:

Expression Value

________ _____ a +=b+c a= 6

b *=c=d+5 b= 18

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References Herbert Schildt: C: The Complete Reference,

4th ed, Osborne Publishing Deitel & Deitel: C How to Program, 4th ed.,

Chapter 3, 4 & 9, Prentice Hall