#include<stdio.h>

#include<stdlib.h>

char *find_char(char const *source_str, char const *desc_str);

int main(void)

{

    char *source_str = "ABCDEF";

    char *desc_str = "MMD";

    char *c = find_char(source_str, desc_str);

    if(c != NULL)

    {

        printf("%c\n", *c);

    }

    else

    {

        printf("IS NULL!\n");

    }

    return EXIT_SUCCESS;

}

char *find_char(char const *source_str, char const *desc_str)

{

    if( (source_str == NULL) || (desc_str == NULL) )

    {

        return NULL;

    }

    int i = ;

    while(*desc_str != '\0')

    {

        while(*source_str != '\0')

        {

            if(*desc_str == *source_str)

            {

                char c = *source_str;

                char *d = &c;

                return d;

            }

            source_str++;

            i++;

        }

        desc_str++;

        source_str -= i;//将source_str的指针置位

        i = ;

    }

    return NULL;

}