basics-guide

Table of Contents

1. Getting Started
2. Use of Library function
3. Decision Control
   1. if
   2. if-else
   3. else if
   4. conditional statements
4. Loops
   1. for
   2. while
   3. do while
   4. continue
   5. break
5. Case control
6. Function
   1. simple function
   2. pass by value
   3. library function
   4. complex function
7. Pointers
8. Recursion
9. Array
   1. simple array
   2. call by value example
   3. call by reference example

Reference

All code taken directly from the book Let Us C - By Yashavant Kanetkar

Getting Started

The basic syntax of C is given below,

# include <stdio.h>
int main( )
{
int p, n ;
float r, si ;
p = 1000 ;
n = 3 ;
r = 8.5 ;
/* formula for simple interest */
si = p * n * r / 100 ;
printf ( "%f\n" , si ) ;
return 0 ;
}

example of taking an input from user

# include <stdio.h>
int main( )
{
int num ;
printf ( "Enter a number: " ) ;
scanf ( "%d", &num ) ;
printf ( "Now I am letting you on a secret...\n" ) ;
printf ( "You have just entered the number %d\n", num ) ;
return 0 ;
}

Use of Library function

Program using the math.h library to perform exponentiation.

# include <math.h>
# include <stdio.h>
int main( )
{
float a ;
a = pow ( 3.0, 2.0 ) ;
printf ( "%f", a ) ;
}

Decision Control

Decision control is implemented using if statement, if-else statement, conditional operators.

if statement

# include <stdio.h>
int main( )
{
int num ;
printf ( "Enter a number less than 10 : " ) ;
scanf ( "%d", &num ) ;
if ( num < 10 )
printf ( "What an obedient servant you are !\n" ) ;
    return 0 ;
}

if-else statement

/* Method – I */
# include <stdio.h>
int main( )
{
    int m1, m2, m3, m4, m5, per ;

    printf ( "Enter marks in five subjects: " ) ;
    scanf ( "%d %d %d %d %d", &m1, &m2, &m3, &m4, &m5 ) ;
    per = ( m1 + m2 + m3 + m4 + m5 ) * 100 / 500 ;

    if ( per >= 60 )
        printf ( "First division\n" ) ;
    else
    {
        if ( per >= 50 )
            printf ( "Second division\n" ) ;
        else
        {
            if ( per >= 40 )
                printf ( "Third division\n" ) ;
            else
                printf ( "Fail\n" ) ;
        }
    }

    return 0 ;
}

else if statement

/* else if ladder demo */
# include <stdio.h>
int main( )
{
    int m1, m2, m3, m4, m5, per ;

    printf ( "Enter marks in five subjects " ) ;
    scanf ( "%d %d %d %d %d", &m1, &m2, &m3, &m4, &m5 ) ;

    per = ( m1+ m2 + m3 + m4+ m5 ) * 100 /500 ;

    if ( per >= 60 )
        printf ( "First division\n" ) ;
    else if ( per >= 50 )
        printf ( "Second division\n" ) ;
    else if ( per >= 40 )
        printf ( "Third division\n" ) ;
    else
        printf ( "fail\n" ) ;

    return 0 ;
}

Conditional operators

/* Insurance of driver - using logical operators */
# include <stdio.h>
int main( )
{
  char sex, ms ;
  int age ;

  printf ( "Enter age, sex, marital status " ) ;
  scanf ( "%d %c %c", &age, &sex, &ms ) ;

  if ( ( ms == 'M') || ( ms == 'U' && sex == 'M' && age > 30 ) || 
      ( ms == 'U' && sex == 'F' && age > 25 ) )
    printf ( "Driver should be insured\n" ) ;
  else
    printf ( "Driver should not be insured\n" ) ;

  return 0 ;
}

Code to calculate gross Salary

/* Calculation of gross salary */
# include <stdio.h>
int main( )
{
    float bs, gs, da, hra ;

    printf ( "Enter basic salary: " ) ;
    scanf ( "%f", &bs ) ;
    
    if ( bs < 1500 )
    {
        hra = bs * 10 / 100 ;
        da = bs * 90 / 100 ;
    }
    else
    {
        hra = 500 ;
        da = bs * 98 / 100 ;
    }
    gs = bs + hra + da ;
    printf ( "gross salary = Rs. %f\n", gs ) ;

    return 0 ;
}

Loops

for loop

/* Calculation of simple interest for 3 sets of p, n and r */
# include <stdio.h>
int main( )
{
    int p, n, count ;
    float r, si ;

    for ( count = 1 ; count <= 3 ; count = count + 1 )
    {
        printf ( "Enter values of p, n, and r " ) ;
        scanf ( "%d %d %f", &p, &n, &r ) ;
        si = p * n * r / 100 ;
        printf ( "Simple Interest = Rs.%f\n", si ) ;
    }
    return 0 ;
}

while loop

/* Calculation of simple interest for 3 sets of p, n and r */
# include <stdio.h>
int main( )
{
    int p, n, count ;
    float r, si ;

    count = 1 ;
    while ( count <= 3 )
    {
        printf ( "\nEnter values of p, n and r " ) ;
        scanf ( "%d %d %f", &p, &n, &r ) ;
        si = p * n * r / 100 ;
        printf ( "Simple interest = Rs. %f", si ) ;
        
        count = count + 1 ;
    }

    return 0 ;
}

do while

/* Execution of a loop an unknown number of times */
# include <stdio.h>
int main( )
{
    char another ;
    int num ;
    do
    {
        printf ( "Enter a number " ) ;
        scanf ( "%d", &num ) ;
        printf ( "square of %d is %d\n", num, num * num ) ;
        printf ( "Want to enter another number y/n " ) ;
        fflush ( stdin ) ;
        scanf ( "%c", &another ) ;
    } while ( another == 'y' ) ;
    
    return 0 ;
}

continue

# include <stdio.h>
int main( )
{
    int i, j ;

    for ( i = 1 ; i <= 2 ; i++ )
    {
        for ( j = 1 ; j <= 2 ; j++ )
        {
            if ( i == j )
            continue ;
            
            printf ( "%d %d\n", i, j ) ;
        }
    }
    return 0 ;
}

break

# include <stdio.h>
int main( )
{
    int num, i ;

    printf ( "Enter a number " ) ;
    scanf ( "%d", &num ) ;

    i = 2 ;
    while ( i <= num - 1 )
    {
        if ( num % i == 0 )
        {
            printf ( "Not a prime number\n" ) ;
            break ;
        }
        i++ ;
    }

    if ( i == num )
        printf ( "Prime number\n" ) ;
}

Case control

# include<stdio.h>
int main( )
{
    int i = 2 ;
    switch ( i )
    {
        case 1 :
            printf ( "I am in case 1 \n" ) ;
            break ;
        case 2 :
            printf ( "I am in case 2 \n" ) ;
            break ;
        case 3 :
            printf ( "I am in case 3 \n" ) ;
            break ;
        default :
            printf ( "I am in default \n" ) ;
    }
    return 0 ;
}

Function

simple function

# include <stdio.h>
void message( ) ; /* function prototype declaration */
int main( )
{
    message( ) ; /* function call */
    printf ( "Cry, and you stop the monotony!\n" ) ;
    return 0 ;
}
void message( ) /* function definition */
{
    printf ( "Smile, and the world smiles with you...\n" ) ;
}

pass by value

/* Sending and receiving values between functions */
# include <stdio.h>
int calsum ( int x, int y, int z ) ;
int main()
{
    int a, b, c, sum ;
    printf ( "Enter any three numbers " ) ;
    scanf ( "%d %d %d", &a, &b, &c ) ;
    sum = calsum ( a, b, c ) ;
    printf ( "Sum = %d\n", sum ) ;
    return 0 ;
}
int calsum ( int x, int y, int z )
{
    int d ;

    d = x + y + z ;
    return ( d ) ;
}

library function

# include <stdio.h>
# include <math.h>

int main( )
{
    float a = 0.5 ;
    float w, x, y, z ;

    w = sin ( a ) ;
    x = cos ( a ) ;
    y = tan ( a ) ;
    z = pow ( a, 2 ) ;
    printf ( "%f %f %f %f\n", w, x, y, z ) ;
    return 0 ;
}

complex value

# include <stdio.h>
void italy() ;
void brazil() ;
void argentina() ;
int main()
{
    printf ( "I am in main\n" ) ;
    italy() ;
    printf ( "I am finally back in main\n" ) ;
    return 0 ;
}
void italy()
{
    printf ( "I am in italy\n" ) ;
    brazil() ;
    printf ( "I am back in italy\n" ) ;
}
void brazil()
{
    printf ( "I am in brazil\n" ) ;
    argentina() ;
}
void argentina()
{
    printf ( "I am in argentina\n" ) ;
}

Pointers

Value of pointer

# include <stdio.h>
int main( )
{
    int i = 3 ;
    printf ( "Address of i = %u\n", &i ) ;
    printf ( "Value of i = %d\n", i ) ;
    return 0 ;
}

swapping of value using pointers

# include <stdio.h>
void swapr ( int *, int * ) ;
int main( )
{
    int a = 10, b = 20 ;
    swapr ( &a, &b ) ;
    printf ( "a = %d b = %d\n", a, b ) ;
    return 0 ;
}
void swapr ( int *x, int *y )
{
    int t ;
    
    t = *x ;
    *x = *y ;
    *y = t ;
}

Recursion

factorial of a number using recursion

# include <stdio.h>
int rec ( int ) ;
int main( )
{
    int a, fact ;

    printf ( "Enter any number " ) ;
    scanf ( "%d", &a ) ;

    fact = rec ( a ) ;
    printf ( "Factorial value = %d\n", fact ) ;
    return 0 ;
}
int rec ( int x )
{
    int f ;

    if ( x == 1 )
        return ( 1 ) ;
    else
        f = x * rec ( x - 1 ) ;
    return ( f ) ;
}

Array

Simple array

# include <stdio.h>
int main( )
{
    int avg, sum = 0 ;
    int i ;
    int marks[ 30 ] ; /* array declaration */
    for ( i = 0 ; i <= 29 ; i++ )
    {
        printf ( "Enter marks " ) ;
        scanf ( "%d", &marks[ i ] ) ; /* store data in array */
    }
    for ( i = 0 ; i <= 29 ; i++ )
        sum = sum + marks[ i ] ; /* read data from an array*/

    avg = sum / 30 ;
    printf ( "Average marks = %d\n", avg ) ;
    return 0 ;
}

Call a element in array by value

/* Demonstration of call by value */
# include <stdio.h>
void display ( int ) ;
int main( )
{
    int i ;
    int marks[ ] = { 55, 65, 75, 56, 78, 78, 90 } ;
    for ( i = 0 ; i <= 6 ; i++ )
        display ( marks[ i ] ) ;
    return 0 ;
}
void display ( int m )
{
    printf ( "%d ", m ) ;
}

Call a element in array by reference

/* Demonstration of call by reference */
# include <stdio.h>
void disp ( int * ) ;
int main( )
{
    int i ;
    int marks[ ] = { 55, 65, 75, 56, 78, 78, 90 } ;
    for ( i = 0 ; i <= 6 ; i++ )
        disp ( &marks[ i ] ) ;
    return 0 ;
}
void disp ( int *n )
{
    printf ( "%d ", *n ) ;
}