c program for the reverse the digits

Question

I am looking for the c program for reverse the digits like ......

if i enter 123456

then the result would be .... 654321

plz any one help...

Answer 1

Use % 10 to get the last digit. Output it. Divide the number by 10 to get all but the last digit. Use % 10 to get the last digit of that. And so on, until the number becomes 0.

Answer 2

Here is a simple solution to this complex problem:

#include <stdio.h>

int main()
{
    int ch;
    ch = getchar();
    if (ch != '\n') {
        main();
        printf("%c", ch);
    }
}

---

A new version that outputs the newline:

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

static void newline(void)
{
    printf("\n");
}

int main()
{
    int ch;
    ch = getchar();
    if (ch != '\n') {
        main();
        printf("%c", ch);
    } else {
        atexit(newline);
    }
}

Answer 3

Read the number in a char array A with scanf("%s", A) or, better, with fgets and output the char array reversed by outputting each character starting from strlen(A) - 1 to 0.

Answer 4

strrev function reverses the string. If performance is not a problem then for instance you can do itoa, then strrev, then atoi. But the task is very simple even without strrev.

Answer 5

Here is another possibility. It is non-recursive, and perhaps a little less code. There is an example in the code comments to explain the logic.

/*
    Example: input = 12345

    The following table shows the value of input and x
    at the end of iteration i (not in code) of while-loop.
    ----------------------
    i   |   input  |    x
    ----------------------
    0       12345       0
    1        1234       5
    2         123      54
    3          12     543
    4           1    5432
    5           0   54321
    ----------------------
*/
uint32_t
reverseIntegerDigits( uint32_t input )
{
    uint32_t x = 0;

    while( input )
    {
        x = 10 * x + ( input % 10 );
        input = input / 10;
    }

    return x;
}