#include <stdio.h>
#include <stdlib.h>


int strlen1(char *st) {
    int length;
    length = 0;
    while (*st != '\0') {
        length++;
        st++;
    }
    return length;
}

char *strcpy1( char *target , char *source ){
    while ((*target = *source) != '\0'){
        target++;
        source++;
    }
return target;
}

int *strstr1( char *string1, char *pattern) {
    int flag1 = 0;
    int i = 0;
    int k = 0;
    int j = 0;

    for (;*string1 != '\0';string1++){
        i++;
            for( j = 0; *(string1+j) == *(pattern+j); j++);
        if (*(pattern+j) == '\0') {
            flag1 = 1;
            k = i;
            break;
        }
    }

    if (flag1 == 1) {
        return k ;
    } else {
        return -1;
    }
}

int main(){
    char *st, *source, *target, *string1, *pattern;
    int k;
    int c;
    source = "cat";
    target = "dog";
    strcpy1(target, source);
    c = strlen1("abcdf");
    printf("%d \n", c);
    printf("%s", target);
    k = strstr1("hello, world", "world");
    printf("%d \n", k);
    return 0;
}