regex.c

// A C program to match wild card characters
// I must have copied this from geeksforgeeks.org
//
#include <stdio.h>
#include <stdbool.h>

// The main function that checks if two given strings match. The first
// string may contain wildcard characters
bool match(char *first, char * second)
{
    // If we reach at the end of both strings, we are done
    if (*first == '\0' && *second == '\0')
        return true;

    // Make sure that the characters after '*' are present in second string.
    // This function assumes that the first string will not contain two
    // consecutive '*'
    if (*first == '*' && *(first+1) != '\0' && *second == '\0')
        return false;

    // If the first string contains '?', or current characters of both
    // strings match
    if (*first == '?' || *first == *second)
        return match(first+1, second+1);

    // If there is *, then there are two possibilities
    // a) We consider current character of second string
    // b) We ignore current character of second string.
    if (*first == '*')
        return match(first+1, second) || match(first, second+1);
    return false;
}

// A function to run test cases
void test(char *first, char *second)
{  match(first, second)? puts("Yes"): puts("No"); }

// Driver program to test above functions
int main()
{
    test("g*ks", "geeks"); // Yes
    test("ge?ks*", "geeksforgeeks"); // Yes
    test("g*k", "gee");  // No because 'k' is not in second
    test("*pqrs", "pqrst"); // No because 't' is not in first
    test("abc*bcd", "abcdhghgbcd"); // Yes
    test("abc*c?d", "abcd"); // No because second must have 2 instances of 'c'
    test("*c*d", "abcd"); // Yes
    test("*?c*d", "abcd"); // Yes
    test("g*e*kss*", "geeksforgeeks"); // Yes
    return 0;
}