Moreover, don’t use C at all if you have the choice. A std::string in C++ makes mincemeat of the boilerplate that C requires for the same code.

In C++, you can make a very simple REPL that is superior to the one in the OP in almost every way.

  #include <iostream>
  #include <string>

  int main() {
    std::string input;

    while (true) {
      std::cout << "> ";
      std::getline(std::cin, input);

      if(input == "exit") {
        return EXIT_SUCCESS;
    } else {
        std::cout << "Unrecognized command: " << input << '\n';
      }
    }
  }

Code quoted from “Setting Up A Better REPL” (https://mikeloomisgg.github.io/2019-04-10-set-up-repl/). It offers good insight into why C is bad in light of the alternatives like Rust and C++.