c program for the reverse the digits

问题

I am looking for the C program for reverse the digits like below:

If i enter:

123456

Then the result would be:

654321

Please help me.

回答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.

回答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);
    }
}

回答3:

If your professor is grading you on performance, then try ggf31416's solution to this problem in another question:

int FastReverse(int num) {
    int res = 0;
    int q = (int)((214748365L * num) >> 31);
    int rm = num - 10 * q;
    num = q;
    if (rm == 0) return -1;
    res = res * 10 + rm;
    while (num > 0) {
       q = (int)((214748365L * num) >> 31);
       rm = num - 10 * q;
       num = q;
       res = res * 10 + rm;
    }
    return res;
}

Optimization^{^®}

^{When it absolutely, positively has to be done this nanosecond.}

回答4:

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;
}

回答5:

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.

回答6:

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.

回答7:

Looks like a very old thread. But I referred the solutions here and had to cook up my own solution after testing the different programs available as solution on this website. I realized that treating the number as int will not yield necessary reversing of digit if the number ends with zero(s). So I decided to treat the number as a string and then reverse the digits. This way, I get exact reverse of the digit from a string standpoint and not a mathematical one that discards zeros at the beginning of a number.

#include <stdio.h>
#include <string.h>

main()
{

    char num[20];
    int x=0,slen;

    printf("Enter the number you want to reverse :");
    scanf("%s",num);
    slen=strlen(num);


    char *pointertoarray = &num[slen];

    for (x=slen;x>=0; x--){ printf("%c",*pointertoarray); pointertoarray--; }
    printf("\n");

}

回答8:

count the number of digits in number and store in count variable
extract individual digits in variable

use the power function.

while(count>=1)
{
  var = num % 10;
  sum = sum + var * pow(10, count - 1);
  num =num / 10;
  count--;
}

来源：https://stackoverflow.com/questions/2351251/c-program-for-the-reverse-the-digits

标签

reverse