diff --git a/task4.cpp b/task4.cpp
new file mode 100644
index 0000000..e8d41d6
--- /dev/null
+++ b/task4.cpp
@@ -0,0 +1,53 @@
+#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 = mystrlen(str2);
+    for (int k = 0; k < j; ++k) {
+        str1[i + k] = str2[k];
+    }
+    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");
+}
\ No newline at end of file