Interview Question for Software Engineer at Google:

I'm no c/c++ person. so here's my solution in java.

public void reverse(final char[] array) {
        final int half = array.length/2;
        final int last = array.length-1;
        for(int i = 0; i < half; i++) {
            final int j = last-i;
            final char ci = array[i];
            final char cj = array[j];
            array[i] = cj;
            array[j] = ci;
        }
    }

More concisely (still Java):

public String reverse(String s){
    char[] a = s.toCharArray();
    int n = a.length, j = n-1;
            for (int i=0; i < n/2; i++){
        char c = a[i]
        a[i] = a[j-i];
        a[j-i] = c;
    }
    return new String(a);
}

C++ Solution. I got this question on another interview albeit with the constraint that I couldn't use any temp variables. So the swapping is done using math:
a = a+b;
b = a-b;
a = a-b;
Will swap a and b!

To convert this into a C solution, pass char* s with the length and use pointers.

void reverse (string &s) {

        int start = 0;
        int end = s.length() - 1;

        while (start < end) {
                s[start] = s[start] + s[end];
                s[end] = s[start] - s[end];
                s[start] = s[start] - s[end];
                start++;
                end--;
        }
}

Thanks all for the nice solutions. There's another good C solution at StackOverflow, and it's allegedly UTF safe: http://stackoverflow.com/questions/198199/how-do-you-reverse-a-string-in-place-in-c-or-c/198264#198264