unsigned int mystrlen(char *s){
    unsigned int i;

    if (s==NULL) {
        return 0;
    }

    for (i=0; s[i]!='\0'; i++);

    return i;
}

char *mystrchr(char *s, char c){
    int i;

    if (s==NULL)
        return NULL;

    for (i=0; s[i]!=c && s[i]!='\0'; i++);

    if (s[i]=='\0')
        return NULL;

    return &s[i];
}

char *mystrcpy(char *dest, char *src){
    int i;

    if (dest==NULL || src==NULL)
        return NULL;

    for (i=0; src[i]!='\0'; i++) {
        dest[i]=src[i];
    }
    dest[i]='\0';

    return dest;
}

char *mystrcat(char *dest, char *src){
    int i,j;

    if (dest==NULL || src==NULL)
        return NULL;

    i=mystrlen(dest);

    for (j=0; src[j]!='\0'; j++) {
        dest[i++]=src[j];
    }
    dest[i]='\0';

    return dest;
}

int mystrcmp(char *s1, char *s2){
    int i;

    if (s1==NULL || s2==NULL) {
        return 0;
    }

    for (i=0; s1[i]!='\0' && s2[i]!='\0' ; i++) {
        if (s1[i]>s2[i]) {
            return 1;
        }
        if (s2[i]>s1[i]) {
            return -1;
        }
    }

    return 0;
}