Switch locks command when entering a letter

Question

I’m making a code that uses switch (because the user can’t give any input) where I need the user to determine if r0 will have the integer value of 1 or 2, any other number will cause the question to be redone. My problem is when a letter is placed, which causes the code to be in a locked loop, some suggestion to fix it?

pergunta1() {
cin >> r0;
switch (r0){
    case 1:
        pergunta2();
    case 2:
        pergunta2();
    default:
        pergunta1();
}

Answer 1

Use a stringstream to receive cin as the stream processes the characters one by one and interrupts the process if there is an invalid character according to the type requested.

#include <iostream>
#include <sstream>
#include <string>

using namespace std;

void pergunta2(void ){
  std::cout << "pergunta2" << std::endl;   
}

void pergunta1(void ) {

      std::cout << "pergunta1" << std::endl; 

      string input;
      getline(cin, input);
      stringstream buffer(input);

      //std::stringstream buffer;
      // Descomente a próxima linha caso r0 ainda não tenha sido declarado
       int r0; 

      //buffer << std::cin;
      buffer >> r0; 

      switch (r0){
          case 1:  // fall through      
          case 2:
              pergunta2();
              break;
          default:
              pergunta1();
       }
   }

int main()
{

    pergunta1();

    return 0;
}

Answer 2

Note the variable declaration r0. Analyzing the switch, it is possible to infer that you have declared the variable r0 with the guy int. This is causing the loop. Try to adapt your code to the following:

void pergunta1() {
    char r0;

    cin >> r0;

    switch (r0){
        case '1':
            pergunta2();
            break;
        case '2':
            pergunta2();    
            break;
        default:
            printf("Valor inválido!\n");
            pergunta1();
    }
}

Note the variable declaration r0, with the guy char. And also in the structure of switch which now has simple quotes to validate the values.

Answer 3

UPDATE

Placing here a robust version of the program that has been posted.

The root cause of the problem (infinite loop) is a conjunction of 2 factors: the unverification of the "Cin >> R0" result, and the use of recursion.

In this situation, when something non-numerical is typed, the program enters an infinite loop.

Keyboard reading is a notoriously difficult task for beginners in both C and C++.

#include <iostream>
#include <string>
using namespace std;

static void pergunta2()
{
  cout << "* pergunta2\n";
}

static void pergunta1()
{
  int r0;
  string resto_da_linha;

  // loop de execucao de pergunta1
  for (;;) // #1
  {

    // leitura e consistencia da digitacao
    for (;;) // #2
    {
      cout << "* digite uma opcao: 1 ou 2: " << flush;
      if (cin >> r0)
      {
        // sucesso na leitura de um numero
        break;
      }
      cout << "* erro, digitacao invalida (digitar apenas numeros)\n";
      cin.clear(); // como houve erro na leitura, precisa limpar o estado de cin

      // cin.ignore(1000, '\n');    // opcao 1 para limpar o buffer de entrada
      getline(cin, resto_da_linha); // opcao 2 para limpar o buffer de entrada
    } // for #2

    // por via das duvidas limpa o buffer de leitura,
    // caso o usuario tenha digitado coisas demais
    // cin.ignore(1000, '\n');
    getline(cin, resto_da_linha);

    switch (r0)
    {
      case 1:
        pergunta2();
        break;
      case 2:
        pergunta2();
        break;
      default:
        cout << "\n* erro, opcao invalida\n\n";
        break;
    } // switch
  } // for #1
} // pergunta1

int main()
{
  pergunta1();
}