need help involving strings and stuff

im still a student in computer science, so my code may look a bit bad :D

my problem is this: i got a code which prints the reverse of a string(eg. input: qwerty output: ytrewq) and when i run it alone in a seperate .c file as the main function, it works fine, but when i include it in my main .c file(which also includes a lot more functions) it goes haywire and prints additional characters in the output.

heres the code

Code:

---

char s[100];   
    int i, j = 0, x = 0;
    printf("\ns? ");
    scanf("%s", &s);


    while(s[x] != '\0')
    {
        j++;
        x++;
    }
    i = 0;
    while(i < j)
    {
        s[i] = s[i] + s[j];
        s[j] = s[i] - s[j];
        s[i] = s[i] - s[j--];
        i++;
    }
    printf("\nReverse string is :%.2s", s+1);

---

it goes fine alone as the main function but when i put it in my main code which looks like this:

Code:

---

#include<stdio.h>
void reverse();

void main()
{
    int function;

    printf("Enter function number: ");
    scanf("%d", &function);

    switch(function)
    {
        case 1:
        {
            reverse();
            break;
        }
}

void reverse()
{
    char s[100];
    int i, j = 0, x = 0;
    printf("\ns? ");
    scanf("%s", &s);


    while(s[x] != '\0')
    {
        j++;
        x++;
    }
    i = 0;
    while(i < j)
    {
        s[i] = s[i] + s[j];
        s[j] = s[i] - s[j];
        s[i] = s[i] - s[j--];
        i++;
    }
    printf("\nReverse string is :%s\n", s+1);;
}

---

idk if the second code works because it doesnt realy look like that but i hope you get the point.

1. You're using scanf with "%s" which expects char* but then you give it the address to your character array, which is char**. Just use

Code:

---

scanf("%s", s);

---

2. What is x being used for?
3. Don't use "%.2s" because it will only print 2 chars of your result.
4. Major problem--> Why do you use s+1? It seems like you want to skip the '\0' that was at the end of the old string, but where is the '\0' at the end of s+1?

For example if you type "qwerty" then the memory in s looks like this:

Before: q, w, e, r, t, y, \0

After: \0, q, w, e, r, t, y

So I guess you thought you can just skip over the '\0' by printing s+1. However, there is not necessarily a '\0' at the end of 'y'. Maybe there will be some of the time, maybe there won't be some of the time. Solution is to back up your j index by one as soon as it sees the '\0'

Code:

---

while(s[j] != '\0')
    {
        j++;
    }
    j--;

    i = 0;
    while(i < j)
    {
        s[i] = s[i] + s[j];
        s[j] = s[i] - s[j];
        s[i] = s[i] - s[j--];
        i++;
    }

---

Now it will work like this:

Before: q, w, e, r, t, y, '\0'
After: y, t, r, e, w, q, '\0'

Then forget about the s+1

Code:

---

printf("Reverse string is: %s\n", s);

---

thanks man! :D