Вторая не очен ьужачная попытка

main.cpp

@@ -0,0 +1,113 @@
+#include <iostream>
+
+using namespace std;
+
+/******************************************************************************
+
+                              Online C++ Compiler.
+               Code, Compile, Run and Debug C++ program online.
+Write your code in this editor and press "Run" button to compile and execute it.
+
+https://www.onlinegdb.com/online_c++_compiler
+
+*******************************************************************************/
+
+#include <cctype>
+#include <cstdlib>
+#include <iostream>
+#include <string>
+
+// std::string kek(std::string strIn, int pos = 0)
+// {
+//     std::cout << strIn << std::endl;
+
+//     for (int i = pos; i < strIn.size(); i++)
+//     {
+//         std::string strNum;
+//         if (std::isdigit(static_cast<unsigned>(strIn[i])))
+//         { // Если число
+//             while (true)
+//             {
+//                 strNum += strIn[i++];
+//                 if (strIn[i] == '[')
+//                     break; // Буквы или цифры начнутся со следующей буквы
+//             }
+//             auto repeat = std::atoi(strNum.c_str());
+//             std::cout << repeat << std::endl;
+
+//         }
+//     }
+
+//     return "return";
+// }
+
+std::string decode(std::string& strIn, std::string::iterator& itr)
+{
+    std::string out;
+
+    while (itr != strIn.end())
+    {
+        std::string strNum;
+        auto repeat = 1;
+
+        auto itr_char = *itr; // DELME
+
+        if (std::isdigit(static_cast<unsigned>(*itr)))
+        {
+            while (*itr != '[')
+            {
+                strNum += *itr++;
+            }
+            repeat = std::atoi(strNum.c_str());
+            // std::cout << repeat << std::endl; // DELME
+            auto tmp = decode(strIn, ++itr);
+
+            for (int i = 0; i < repeat; ++i)
+                out += tmp;
+
+        }
+
+        if (*itr == ']')
+        {
+            return out; // нужно будет вернуть подстроку
+        }
+        else
+            out += *itr;
+
+        ++itr;
+    }
+
+    return out;
+}
+
+std::string kek(std::string strIn)
+{
+    std::cout << strIn << std::endl;
+    auto itr = strIn.begin();
+
+    return decode(strIn, itr);
+}
+
+int main()
+{
+    std::string strIn;
+
+    strIn = "3[a2[c]]";
+    std::cout << kek(strIn) << std::endl;
+
+    strIn = "c2[a]3[b]c";
+    std::cout << kek(strIn) << std::endl;
+
+    strIn = "c2[a3[b]]c";
+    std::cout << kek(strIn) << std::endl;
+
+    strIn = "231[ab]";
+    std::cout << kek(strIn) << std::endl;
+
+    strIn = "3[b15[a]]";
+    std::cout << kek(strIn) << std::endl;
+
+    // std::string wait;
+    // std::cin >> wait;
+    return 0;
+}