The sample code to pointer position of specific char in a string.

Char_Finder.c

size_t strlength(char const *string) {
    int length = 0;
    while (*string++ != '\0') {
        length += 1;
    }
    
    return length;
}

char *find_char(char const *source, char const *chars) {
    char const *competitor = NULL;
    char const *finding = NULL;
    size_t sourceLen = strlength(source);
    
    while (*(competitor = chars++) != '\0') {
        while (*(finding = source++) != '\0' && *finding != *competitor);
        source = source - (sourceLen + 1);
    
        if (*finding != '\0') {
            break;
        }
    }
    
    return (char *)finding;
}