Converting int to char and reversing

Question

Task is to convert int to char . Here is my code for converting

#include <conio.h>
#include <stdio.h>

main(void)
{
int number,reserve ;
scanf_s("%d",&number);
if (number > 0 || number == 0)
{
    do
    {
        reserve = number % 10;
        printf("%c", reserve + '/0');
        number /= 10;
    } while (number != 0);
}
else
{
    number *= -1;
    printf("-");
    do
    {
        reserve = number % 10;
        printf("%c", reserve + '/0');
        number /= 10;
    } while (number != 0);

}
_getch();
return 0;
}

The problem is this is printing the result in the reversed of what I want. So I'm searching for a way to reverse it back. However my code is printing char by char. Probably I just need to save all chars into some string but I`m not sure of how do it. Appreciate any help.

So you want to store those characters and print them in reverse order? — hbagdi, Dec 02 '16 at 03:55
Have you tried storing it in an array and then finally printing the array in the reverse order? Or a stack? — hbagdi, Dec 02 '16 at 03:57
i thought about array but i don't know how write it properly — andrewand, Dec 02 '16 at 04:00
Note: `number *= -1;` is UB if `number == INT_MIN` with 2's complement. — chux - Reinstate Monica, Dec 02 '16 at 04:04
@chux: Probably yes, but do you really expect andrewand to understand that problem now? You could explain that to him in two years, but today, it's not the right time to tell him this. — Bodo Thiesen, Dec 02 '16 at 04:05
@BodoThiesen Comments are a good place for discussion abouts issues about the post like [relevant but minor or transient information](http://stackoverflow.com/help/privileges/comment) and comments/answers. Comments about [OP and SO users](http://stackoverflow.com/questions/40924503/converting-int-to-char-and-reversing#comment69060791_40924503) are better handled in chat or meta. — chux - Reinstate Monica, Dec 02 '16 at 04:17

hbagdi · Accepted Answer · 2016-12-02T04:17:53.163

1

Have you tried storing them in an array and printing the array in reverse?

#include <stdio.h>

int main(void)
{
    int number,reverse,i ;
    scanf("%d",&number);
    char string[20];
    int index = 0;
    if (number< 0){
       number *= -1;
       printf("-");
    }
    do
    {
        reverse = number % 10;
        //printf("%c", reverse);
        string[index++] = reverse;
        number /= 10;
    } while (number != 0);

    for (i = index ; i >= 0 ; i--)
        printf("%c", string[i]);
    return 0;
}

edited Dec 02 '16 at 04:17

answered Dec 02 '16 at 04:05

hbagdi

485
6
18

getting hundreds of mistakes – andrewand Dec 02 '16 at 04:13
1

andrewand, this gives you more than enough help on what you should be doing. Try and figure out minor errors. I've updated the answer again. – hbagdi Dec 02 '16 at 04:19
Finally i found what is wrong , well at least i have working code now. Appreciate – andrewand Dec 02 '16 at 04:24

score 0 · Answer 2 · answered Dec 02 '16 at 04:03

As you assumed in your question, you need to store the characters to print them reverse.

Using an array for this task is quite simple:

// I never know how much memory I need ...
char reverse[200];
int i = 0;
reverse[i++] = next calculated character

later

while (i) {
    print reverse[--i];
}

score 0 · Answer 3 · answered Dec 02 '16 at 15:19

This method should suffice in converting an integer to a string without using any standard library functions.

void ReverseString(char *sBuf, int iLength)
{
    char *String1 = NULL;
    char *String2 = NULL;

    for (String1 = sBuf, String2 = sBuf + iLength - 1; String2 > String1; ++String1, --String2)
    {
        *String1 ^= *String2;
        *String2 ^= *String1;
        *String1 ^= *String2;
    }
}

int YourVeryOwn_itoa(int iINValue, char *sOUTValue)
{
    unsigned short writePosition = 0;

    if (iINValue < 0)
    {
        sOUTValue[writePosition++] = '-';
    }

    do
    {
        sOUTValue[writePosition++] = (unsigned char)48 + (iINValue % 10);
    } while ((iINValue /= 10) > 0);

    sOUTValue[writePosition] = '\0';

    ReverseString(sOUTValue, writePosition);

    return writePosition;
}

void main()
{
    char buf[255];
    YourVeryOwn_itoa(123456789, buf);
    printf("%s", buf);
}

are you trying to do [xor swap](https://en.wikipedia.org/wiki/XOR_swap_algorithm)? it's a very bad idea. [`void main()`](http://stackoverflow.com/q/204476/995714) is also a bad idea — phuclv, Dec 02 '16 at 15:29
The previous rendition I did here actually mentioned that XOR was a bad idea for all of the known reasons (I like it because its quick to type). Also, as an example void main() is perfectly acceptable. — NTDLS, Dec 03 '16 at 01:38

Converting int to char and reversing

3 Answers3