C Program to Reverse a Given Number

September 28, 2022

Program to Reverse a Number in C

In this post we will learn how to reverse a number in c. For example, if a user will enter 4567 as input then 7654 will be printed as output. This C program accepts an integer and reverse it.
c program to reverse a number
While loop in C

Working:-

For a user input num

  • Initialize reverse = 0, rem
  • Extract the last digit of num (rem = num % 10)
  • Multiply reverse with 10 & add remainder (reverse = reverse * 10 + rem)
  • Reduce the original number (num = num/10)
  • Keep doing this until original number becomes 0
Reverse a given number in C

C program:-

Run

#include<stdio.h>

//main program
int main ()
{
  //variables initialization
  int num, reverse = 0, rem;
  num=1234;
  printf("The number is: %d\n",num);
  
 
  //loop to find reverse number
    while(num != 0)
    {
      rem = num % 10;
      reverse = reverse * 10 + rem;
      num /= 10;
    };
 
  //output
  printf("Reverse: %d\n",reverse);
  
  return 0;
}
// Time complexity O(N)
// Space complexity : O(1)

Output:-

The number is: 1234
Reverse: 4321
While loop in C

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Method 2

This method uses a recursive approach.

Code

Run

#include<stdio.h>

int getReverse(int num, int rev){
if(num == 0)
return rev;

int rem = num % 10;
rev = rev * 10 + rem;

return getReverse(num / 10, rev);
}

//main program
int main ()
{
int num, rev = 0;
num=1234;
printf("The number is: %d\n",num);

printf("Reverse: %d", getReverse(num, rev));
}

Output

The number is: 1234
Reverse: 4321
Software Engineering SDLC

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