Reverse an Integer
#include <stdio.h>
int main() {
int n, reverse = 0, remainder;
printf("Enter an integer: ");
scanf("%d", &n);
while (n != 0) {
remainder = n % 10;
reverse = reverse * 10 + remainder;
n /= 10;
}
printf("Reversed number = %d", reverse);
return 0;
}
Output
Enter an integer: 2345 Reversed number = 5432
This program takes integer input from the user. Then the while loop is used until n != 0 is false (0).
In each iteration of the loop, the remainder when n is divided by 10 is calculated and the value of n is reduced by 10 times.
Inside the loop, the reversed number is computed using:
reverse = reverse * 10 + remainder;
Let us see how the while loop works when n = 2345.
| n | n != 0 | remainder | reverse |
|---|---|---|---|
| 2345 | true | 5 | 0 * 10 + 5 = 5 |
| 234 | true | 4 | 5 * 10 + 4 = 54 |
| 23 | true | 3 | 54 * 10 + 3 = 543 |
| 2 | true | 2 | 543 * 10 + 2 = 5432 |
| 0 | false | - | Loop terminates. |
Finally, the reverse variable (which contains the reversed number) is printed on the screen.