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Chapter 1 Basic C Programming

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1st C Program hello.c /* My first C programming */#include<stdio.h>int main(){ printf(“Hello World”); return 0;}

/* My first C programming */#include<stdio.h>int main(){ printf(“Hello World”); return 0;}

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Source file Executable file/* My first C programming */#include<stdio.h>int main(){ printf(“Hello World”); return 0;}

/* My first C programming */#include<stdio.h>int main(){ printf(“Hello World”); return 0;}

CompileCompile LinkLink Executable fileExecutable file

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Compiling using gcc $ gcc hello.c //CompileOutput is a.out $ ./a.out //Run ProgramHello World

$ gcc -o hello hello.c //CompileOutput is hello $ ./helloHello World

$ gcc –Wall –o hello hello.c //Compile with warning$ ./helloHello World

output

output

output

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2nd C program add.c

/* Addition program */

#include <stdio.h>

int main()

{ int x,y,z;

printf(“Enter first integer: ”);

scanf(“%d”, &x);

printf(“Enter second integer: ”);

scanf(“%d”, &y);

z = x + y;

printf(“Sum is %d \n”, z);

return 0;

}

/* Addition program */

#include <stdio.h>

int main()

{ int x,y,z;

printf(“Enter first integer: ”);

scanf(“%d”, &x);

printf(“Enter second integer: ”);

scanf(“%d”, &y);

z = x + y;

printf(“Sum is %d \n”, z);

return 0;

}

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Compile and Run

$ gcc –Wall –o add add.c

$ ./addEnter first integer: 2

Enter second integer: 3

Sum is 5

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Memory as Many Boxes Each box is labelled with an identifier; it is the

name of the box.e.g. x, y, z

The address of a box is & and its name e.g. &x, &y, &z;

Boxes are typed (e.g. int, float, etc.). This specifies their size and shape

Boxes contain values (e.g. 5, 3.4)

C Programs Mess With Boxes

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#include<stdio.h>

int main()

{ int a, b;

printf(“Enter 2 nums and I will tell you the relationships they satisfy: “);

scanf(“%d%d”,&a, &b);

if(a == b)

printf(“%d is equal to %d\n”,a,b);

if(a != b)

printf(“%d is not equal to %d\n”,a,b);

if(a < b)

printf(“%d is < than %d\n”,a,b);

3rd C Program bigger.c

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if(a > b)

printf(“%d is > than %d\n”,a,b);

if(a <= b)

printf(“%d is <= to %d\n”,a,b);

if(a >= b)

pritnf(“%d is >= to %d\n”,a,b);

return 0;

}

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Compile and Run

$ gcc –Wall –o bigger bigger.c

$ ./biggerEnter two integers, and I will tell you the relationships they satisfy:

3

7

3 is not equal to 7

3 is < than 7

3 is <= to 7

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A C Program ‘Skeleton’

/* Name, student no. (E-mail addr.) Date Description of Code (5-10 lines)*/#include<stdio.h>int main(){ /* declare some variables */ /* do something */ return 0;}

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Compile and Execute:

$ gcc –Wall –o skeleton skeleton.c

$ ./skeleton

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How to Start Writing a Program

Program = Algorithm + Data Structures Algorithm:

a series of functions, each using a mix of sequencing, branches, loops, recursion and other functions

Data Structures: they reflect the structure of the data in the

Problem Statement

e.g int, float, arrays, struct, etc

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Control Flow

Sequence Choice

if-elseswitch-case

Loop forwhiledo-while

Recursion

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The if statement

:scanf(“%d”, &grade);

if(grade >= 60)

printf(“Passed \n”);

else {

printf(“Failed \n”);

printf(“Repeat Course \n”);

}

:

:scanf(“%d”, &grade);

if(grade >= 60)

printf(“Passed \n”);

else {

printf(“Failed \n”);

printf(“Repeat Course \n”);

}

:

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:scanf(“%d”, &temp);

if(temp < 0)

setting = setting + 20;

else if(temp < 10)

setting = setting + 10;

else

setting = setting + 1;

:

:scanf(“%d”, &temp);

if(temp < 0)

setting = setting + 20;

else if(temp < 10)

setting = setting + 10;

else

setting = setting + 1;

:

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The switch statement

For multiple choices:

condition

task-A task-B task-C

c1 c2 c3

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switch(int-expression) {

case c1: task-A; break;

case c2: task-B; break;

case c3: task-C; break;

:

}

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Ex. Counting Letter Grades

/* Counting letter grades */

#include<stdio.h>

int main()

{

int grade;

int acount=0, bcount=0, ccount=0,

dcount=0, fcount=0;

printf("Enter the letter grades.\n");

printf("Enter EOF to end.\n");

:

/* Counting letter grades */

#include<stdio.h>

int main()

{

int grade;

int acount=0, bcount=0, ccount=0,

dcount=0, fcount=0;

printf("Enter the letter grades.\n");

printf("Enter EOF to end.\n");

:

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while((grade = getchar()) != EOF) { switch(grade) { case 'A': case 'a': ++acount; break; case 'B': case 'b': ++bcount; break; case 'C': case 'c': ++ccount; break; case 'D': case 'd': ++dcount; break;

case 'F': case 'f': ++fcount; break; case '\n': case '': break; default: printf("Incorrect letter grade entered\n Enter a new grade\n"); break;

}}

while((grade = getchar()) != EOF) { switch(grade) { case 'A': case 'a': ++acount; break; case 'B': case 'b': ++bcount; break; case 'C': case 'c': ++ccount; break; case 'D': case 'd': ++dcount; break;

case 'F': case 'f': ++fcount; break; case '\n': case '': break; default: printf("Incorrect letter grade entered\n Enter a new grade\n"); break;

}}

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printf("\nThe totals for each letter grade are: \n");

printf("A: %d \n", acount);

printf("B: %d \n", bcount);

printf("C: %d \n", ccount);

printf("D: %d \n", dcount);

printf("F: %d \n", fcount);

return 0;

}

printf("\nThe totals for each letter grade are: \n");

printf("A: %d \n", acount);

printf("B: %d \n", bcount);

printf("C: %d \n", ccount);

printf("D: %d \n", dcount);

printf("F: %d \n", fcount);

return 0;

}

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Some Points

Very common coding style:

while((grade = getchar()) != EOF)

getchar() reads the next character as an integer and assigns it to grade

EOF is an integer constant representing the end-of-file value. Defined in stdio.h

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Output from letter grades program

Enter the letter grades.

Enter EOF to end input. A B C C A X Incorrect letter grade entered. Enter a new grade. D

(for winOS type ctrl+z to exit /

for unix type ctrl+d to exit)

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Totals for each letter grade were: A: 2

B: 1

C: 2

D: 1

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/* sum between 1 and 10 */ #include<stdio.h>

int main()

{ int i = 1, sum = 0;

while(i <= 10) {

sum = sum + i;

i = i + 1;

}

printf("Sum is %d\n",sum);

return 0;

}

/* sum between 1 and 10 */ #include<stdio.h>

int main()

{ int i = 1, sum = 0;

while(i <= 10) {

sum = sum + i;

i = i + 1;

}

printf("Sum is %d\n",sum);

return 0;

}

The while statement sum.c

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Compile and run

$ gcc -Wall –o sum sum.c

$ ./sumSum is 55

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#include<stdio.h>

int main()

{ int count;

for(count = 1; count <= 10; count++)

printf("%d \n",count);

return 0;

}

#include<stdio.h>

int main()

{ int count;

for(count = 1; count <= 10; count++)

printf("%d \n",count);

return 0;

}

final value

increment

initialvalue

test forcontinuing

The for statement

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for(expr1; expr2; expr3)

statement;

is equivalent to:

expr1;

while(expr2) {

statement;

expr3;

}

The for is a sort of while

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FunctionFUNCTIONS IN CFUNCTIONS IN C

PROGRAMMER DEFINEDFUNCTION

PROGRAMMER DEFINEDFUNCTION

C STANDARDLIBRARY

C STANDARDLIBRARY

INCLUDEHEADER FILE

#include<stdio.h>

INCLUDEHEADER FILE

#include<stdio.h>

FUNCTION PROTOTYPE

int add(int a, int b);

FUNCTION PROTOTYPE

int add(int a, int b);

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C Standard Library

#include<stdio.h>

#include<math.h>

int main()

{

printf("%f", sqrt(16.0));

return 0;

}

#include<stdio.h>

#include<math.h>

int main()

{

printf("%f", sqrt(16.0));

return 0;

}

header file

Call function

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Programmer defined function /* Finding the maximum of three integers */

#include<stdio.h>

int maximum(int x, int y, int z);

int main()

{ int a, b, c;

printf("Enter three integers: ");

scanf("%d%d%d",&a,&b,&c);

printf("Maximum is %d\n“,

maximum(a,b,c));

return 0;

}

/* Finding the maximum of three integers */

#include<stdio.h>

int maximum(int x, int y, int z);

int main()

{ int a, b, c;

printf("Enter three integers: ");

scanf("%d%d%d",&a,&b,&c);

printf("Maximum is %d\n“,

maximum(a,b,c));

return 0;

}

function prototype

Call function

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Function definition int maximum(int x, int y, int z) /*returns the biggest of x, y and z */

{

if(x > y && x > z)

return x;

else if ( y > z)

return y;

else

return z;

}

int maximum(int x, int y, int z) /*returns the biggest of x, y and z */

{

if(x > y && x > z)

return x;

else if ( y > z)

return y;

else

return z;

}

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Enter three integers: 22 85 17

Maximum is 85

Execution

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Array

An array is a data structure which can hold a sequence of values.

The array C[ ] holds 3 integer values:

C[1]

-45

6

72C[2]

C[0]

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Ex. Array/* Initialize array s to the even integers

from 2 to 20 */

#include<stdio.h>#define SIZE 10int main(){ int s[SIZE], j; for(j = 0; j < SIZE; j++) s[j] = 2 + 2 * j; printf("%s%13s \n","Element","Value");

for(j = 0; j < SIZE; j++) printf("%7d%13d \n",j, s[j]); return 0;}

/* Initialize array s to the even integers from 2 to 20 */

#include<stdio.h>#define SIZE 10int main(){ int s[SIZE], j; for(j = 0; j < SIZE; j++) s[j] = 2 + 2 * j; printf("%s%13s \n","Element","Value");

for(j = 0; j < SIZE; j++) printf("%7d%13d \n",j, s[j]); return 0;}

Typical rangeexpression

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Output:

Element Value

0 2

1 4

2 6

: :

9 20

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Functions using Arrays

/* A Program which illustrates the differences between passing an array to a function and passing an array element */

#include<stdio.h>

#define SIZE 5

void modifyArray(int b[], int size);

void modifyElement(int e);

:

/* A Program which illustrates the differences between passing an array to a function and passing an array element */

#include<stdio.h>

#define SIZE 5

void modifyArray(int b[], int size);

void modifyElement(int e);

:

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int main()

{

int a[SIZE] = {0,1,2,3,4};

int i;

printf("The values of the original array are: \n");

for(i = 0; i<SIZE; i++)

printf("%3d",a[i]);

printf("\n");:

int main()

{

int a[SIZE] = {0,1,2,3,4};

int i;

printf("The values of the original array are: \n");

for(i = 0; i<SIZE; i++)

printf("%3d",a[i]);

printf("\n");:

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modifyArray(a, SIZE); printf("The values of the modified array are: \n");

for(i=0; i<SIZE; i++) printf("%3d", a[i]); printf("\n"); printf("The value of a[3] is %d\n",a[3]); modifyElement(a[3]); printf("The value of a[3] is %d\n",a[3]); return 0;}

modifyArray(a, SIZE); printf("The values of the modified array are: \n");

for(i=0; i<SIZE; i++) printf("%3d", a[i]); printf("\n"); printf("The value of a[3] is %d\n",a[3]); modifyElement(a[3]); printf("The value of a[3] is %d\n",a[3]); return 0;}

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void modifyArray(int b[], int size)

{ int j;

for(j=0; j<size; j++)

b[j] *= 2;

}void modifyElement(int e)

{

printf("Value in modifyElement =%d\n", e*=2);

}

void modifyArray(int b[], int size)

{ int j;

for(j=0; j<size; j++)

b[j] *= 2;

}void modifyElement(int e)

{

printf("Value in modifyElement =%d\n", e*=2);

}

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The call to the function modifyArray() is: modifyArray(a, SIZE);

C treats array arguments differently .

Any changes to the elements of a[] will be retained when the function returns.

This is call by reference.

Passing Arrays to Functions

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Output:

The values of the original array are: 0 1 2 3 4

The values of the modified array are:

0 2 4 6 8

The value of a[3] is 6

Value in modifyElement is 12

The value of a[3] is 6

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A string is a sequence of characters which end with the NULL character ‘\0’.

e.g.

"Hello"

"234-56789 Call"

"9"

What is a String?

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Use:char color[] = "blue";

Or equivalence :

char color[] = {‘b’,‘l’,‘u’,‘e’,‘\0’};

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String Manipulation Copy a string: strcpy()

Concatenating strings: strcat()

Comparing strings: strcmp()

Searching a string: strchr()

String Length: strlen()

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#include<stdio.h> #include<string.h>

int main()

{ char x[]= "Happy birthday to you";char y[25];

printf("String in x is: %s\n

String in y is: %s\n", x, strcpy(y,x));

return 0;

}

#include<stdio.h> #include<string.h>

int main()

{ char x[]= "Happy birthday to you";char y[25];

printf("String in x is: %s\n

String in y is: %s\n", x, strcpy(y,x));

return 0;

}

Copying a string: strcpy()

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Output:String in x is Happy Birthday to YouString in y is Happy Birthday to You

Function prototype in string.h: char *strcpy(char *s1,const char *s2);

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Comparing Strings: strcmp() int strcmp(const char *s1,const char *s2);

Compares the string s1 to the string s2 Returns <0 if s1 < s2

0 if s1 == s2

>0 if s1 > s2

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Using strcmp() #include<stdio.h>#include<string.h>int main(){ char s1[] = "Happy New Year"; char s2[] = "Happy New Year"; char s3[] = "Happy Holidays"; printf("%s%s\n %s%s\n %s%s\n %s%2d\n %s%2d\n %s%2d\n", "s1 = ",s1, "s2 = ",s2, "s3 = ",s3, "strcmp(s1,s2) = ",strcmp(s1,s2), "strcmp(s1,s3) = ",strcmp(s1,s3), "strcmp(s3,s1) = ",strcmp(s3,s1), return 0; }

#include<stdio.h>#include<string.h>int main(){ char s1[] = "Happy New Year"; char s2[] = "Happy New Year"; char s3[] = "Happy Holidays"; printf("%s%s\n %s%s\n %s%s\n %s%2d\n %s%2d\n %s%2d\n", "s1 = ",s1, "s2 = ",s2, "s3 = ",s3, "strcmp(s1,s2) = ",strcmp(s1,s2), "strcmp(s1,s3) = ",strcmp(s1,s3), "strcmp(s3,s1) = ",strcmp(s3,s1), return 0; }

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Output:

s1 = Happy New Year

s2 = Happy New Year

s3 = Happy Holidays

strcmp(s1,s2) = 0

strcmp(s1,s3) = 6

strcmp(s3,s1) = -6

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Coding strcmp()

The array version:int strcmp(const char *s, const char *t)

{ int i;

for(i=0; s[i] == t[i]; i++)

if(s[i] == ‘\0’)

return 0;

return s[i] – t[i];

}

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Searching a String: strchr() #include <stdio.h>#include <string.h>

int main(){ char *rest, *sh = "Hello"; char c = 'l';

rest = strchr(sh, c); printf("%s", rest); /* gives llo */ return 0;}

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Function prototype in string.h:char *strchr(const char *s, int c);

‘h’ ‘e’ ‘l’ ‘l’ ‘o’ ‘\0’

shrest