Write a function that takes a string as input and returns the string reversed.
 Example:
 Given s = "hello", return "olleh". 

char* reverseString(char* s) 
{
    char tmp;
    int end = strlen(s) - 1;
    int start = 0;
    while(start < end)
    {
        tmp = s[start];
        s[start++] = s[end];
        s[end--] = tmp;
    }
    return s;
    
}