Program in C to reverse a given Number

Below is the C program to reverse a given number. This C program will accept a number (in a variable named “num”) and performs an operation to reverse the number.

#include <stdio.h>
#include <stdlib.h>

int main(void) {

	int num=1234, newNum=0;

	while(num!=0){
	newNum=newNum*10 + num%10;
	num=num/10;
	}

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

	return 1;
}

Output: 4321

Explanation:

The statement while(num!=0) will be executed till value of num !=0

num%10 (read as num mod 10) will return the last digit. So in 1st iteration, it will return 4.

So, newNum will become–> 0*10 + 4 –>4

Next line i.e. num/10 will return 123

In the 2nd Iteration, newNum=4*10 + (num%10) –> 4*10 + 3 –> 43 and num = 123/10 = 12.

This loop continues until value of num becomes zero.

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9 Responses

  1. Anonymous says:

    It would be helpfull if every line’s function is explained.

  2. LearnCOnline says:

    The statement while(num!=0) will be executed till value of num !=0
    num%10 (read as num mod 10) will return the last digit.
    So in 1st iteration, it will return 4.
    So newNum will become–> 0*10 + 4 –>4
    next line i.e. num/10 will return 123

    2nd Iteration:
    newNum=4*10 + (num%10)–>4*10 + 3 –>43
    num = 123/10 = 12

    This loop continues until value of num becomes zero.
    Hope its clear.

  3. Dennis says:

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  4. Anonymous says:

    #include
    #include
    #include
    #include

    void main()
    {
    int num1, num2;
    char str[10];
    clrscr();

    printf(“\nEnte the Number : “);
    scanf(“%d”,&num1);

    sprintf(str,”%d”,num1);

    strrev(str);

    num2 = atoi(str);

    printf(“\nReversed Number : “);
    printf(“%d\n”,num2);
    getch();
    }
    (i think itz btr)

  5. Anonymous says:

    what about the reverse of a string????

  6. Anonymous says:

    Good explanation for reverse the number

  7. LearnCOnline says:

    Thank you everyone for the wonderful comments. I hope this website is helping every one out there.

    If you like this website, kindly share it with everyone.

    Thanks,
    LearnCOnline Team

  8. shanth says:

    while(num!=0){
    rev=num%10;
    num=num/10;
    }
    print rev and watch

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