#include <stdio.h>
 
/* Search a string for matching parentheses.  If the parentheses match, returns a
 * pointer that addresses the nul terminator at the end of the string.  If they
 * don't match, the pointer addresses the first character that doesn't match.
 */
const char *match(const char *str)
{
        if( *str == '\0' || *str == ')' ) { return str; }
        if( *str == '(' )
        {
                const char *closer = match(++str);
                if( *closer == ')' )
                {
                        return match(++closer);
                }
                return str - 1;
        }
 
        return match(++str);
}
 
 
int main(void)
{
    int index;
    const char *test[] = {
            "())(", ")(", "))(", "(()"
    };
 
    for( index = 0; index < sizeof(test) / sizeof(test[0]); ++index ) {
            const char *result = match(test[index]);
 
            printf("%s:\t", test[index]);
            *result == '\0' ? printf("Good!\n") :
                    printf("Bad @ char %zu\n", result - test[index] + 1);
    }
}