C Program To Reverse a Number

If a integer number is input through the keyboard, write a program to reverse the input number and display it on the console window.

For Example: If user enters 135, reversed number must be 531.

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Note: We assign variable reverse = 0 to avoid garbage values in variable reverse.

Reversing a Number Logic

If user enters 456, we apply the modulo division to get the individual values.
Ex:
456 % 10 = 6
45 % 10 = 5
4 % 10 = 4

After each iteration of while loop we add the reminder to the previous value of variable reverse. We also multiply the variable reverse with 10, to increment the decimal place.

We get 456, 45 and 4 by dividing the original value by 10.
Ex:
456 user entered value.
456 / 10 = 45
45 / 10 = 4

Now the reverse:

reverse = (reverse * 10 ) + rem;

06 = (010) + 6
65 = (610) + 5
654 = (65*10) + 4

So finally the reversed number is 654.

Video Tutorial: C Program To Reverse a Number

Source Code: C Program To Reverse a Number

#include<stdio.h>

int main()
{
    int num, reverse = 0, rem;

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

    while(num)
    {
        rem = num % 10;
        reverse = (reverse * 10) + rem;
        num     = num / 10;
    }

    printf("Reversed number is %d\n", reverse);

    return 0;
}

Output 1:
Enter a integer number
1023
Reversed number is 3201

Output 2:
Enter a integer number
159
Reversed number is 951

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