Problem with condition no While in C++

Question

Problem with condition no While in C++

Hello, I am studying from Bjarne's book "PROGRAMMING Principles and practice Using C++". I'm trying to do drill number 1 of Chapter Four. The exercise says to make a program that consists of a while-loop that reads and prints two integers and stops when it is written|, however, when I write | (or anything other than a number) the program stays in an infinite loop. If anyone can explain to me what is wrong with my code, I have already tried to read in book about conversions from int to char and vice versa and even then the error persists, take a look.

#include <...\Projects\std_lib_facilities.h>

int main()
{
    //drill's
    //1 - inicio

    /*escrever um programa que consiste em um while-loop que leia dois int e termine quando 
é escrito |  */

    int n=0, n1=0;

    cout << "Write a int. To stop the program hit |";

    while (n != '|' || n1 != '|' )
    {
        cin >> n >> n1;

        system("cls");

        cout << n << " " << n1 << "\n";
    }
}

1

while c++14

Author: Arubu, 2016-02-01

Source

1 answers

score 1 · Accepted Answer

As per the SO post (in English):

Https://stackoverflow.com/questions/10349857/how-to-handle-wrong-data-type-input

The reason the program goes into infinite looping is because of a flag (flag) of invalid device input std:: cin .

What needs to be done is to clear the flag and discard the invalid entry from the input buffer.

After correction, the code is like this:

while (n != '|' || n1 != '|')
{
    // limpa a flag
    std::cin.clear(); 

    // Descarta a entrada
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

    std::cin >> n >> n1;

    system("cls");

    std::cout << n << " " << n1 << "\n";
}

The "wrong" input is occurring because of reading a (type) character "| " in a variable of type numeric n or n1.

For more details:

C++ FAQ

Other possibilities to correct:

read content | for a variable type char
read each value to a buffer of type string and then convert to integer with the function std:: stoi

Update:

After applying the second correction suggestion, the looping looks like this:

int n = 0, n1 = 0;

std::string buffer;

std::cout << "Write a int. To stop the program hit |";
while (n != '|' || n1 != '|')
{
    // Lê a primeira entrada
    std::cin >> buffer;

    // Se for um "|", sai do looping
    if (buffer == "|")
        break;
    // Converte para inteiro
    n = std::stoi(buffer);

    // Lê a segunda entrada
    std::cin >> buffer;

    // Se for um "|", sai do looping
    if (buffer == "|")
        break;

    // Converte para inteiro
    n1 = std::stoi(buffer);

    // Limpa a fila std::cin
    std::cin.clear();
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    // std::cin >> n >> n1;

    //system("cls");

    std::cout << n << " " << n1 << "\n";
}

Even with this fix, the above code is still subject to other errors.

Below is a reading suggestion to better understand how the data input and output system works in C++:

Data input and output