#pragma warning(disable : 4996)
#define SIZE 80
#include <iostream>
using namespace std;

int mystrlen(const char* str) {
    int len = 0;
    for (; str[len] != '\0'; ++len) {}
    return len;
}

char* mystrcat(char* str1, const char* str2) {
    int i = mystrlen(str1);
    int j;
    for (j = 0; str2[j] != '\0'; ++j) {
        str1[i + j] = str2[j];
    }
    str1[i + j] = '\0';
    return str1;
}

char* mystrchr(char* str, char s) {
    for (int i = 0; str[i] != '\0'; ++i) {
        if (str[i] == s) {
            return &str[i];
        }
    }
    return 0;
}

int main() {
    char str1[SIZE];
    char str2[SIZE];
    cout << "Input first string: ";
    cin.getline(str1, SIZE);
    cout << "Input second string: ";
    cin.getline(str2, SIZE);

    cout << "mystrlen(str1): " << mystrlen(str1) << endl;
    cout << "mystrcat(str1, str2): " << mystrcat(str1, str2) << endl;

    char ch;
    cout << "Input char to search in str1: ";
    cin >> ch;
    char* f = mystrchr(str1, ch);
    if (f) {
        cout << "mystrchr(str1, '" << ch << "): " << f << endl;
    }
    else {
        cout << "mystrchr(str1, '" << ch << "): 0" << endl;
    }
    system("pause");
}