[N.N.P]

Hi, im having a very basic problem with all programs i write to run in a console window. If I dont use cin.get() the window just closes. Is this normal? if it is then I have another problem/question. At what stage of the program should I put cin.get(). for example, in this program (a very basic calculator) I have to put it in two different places to get the console window to stay open. Why is this, I thought i should only have to put it in at the end and it should wait for me to press return before exiting.

#include <iostream>


using namespace std;

int main()
{
    float num1, num2; 
    char op;
    
    cout<<"Please enter calculation"<<endl;
    cin>>num1>>op>>num2;
    cin.get(); //why do I need cin.get() in two places? here.....
    
    if (op == '+') {
        cout<<"the answer is"<<num1 + num2<<endl;
        } 
    else if (op == '-') {
        cout<<"the answer is"<<num1 - num2<<endl; 
    } else if (op =='*') {
        cout<<"the answer is"<<num1 * num2<<endl;
    } else if (op == '/') {
        cout<<"the answer is "<<num1 / num2<<endl; 
    } else {
        cout<<"You have entered an invalid statement"<<endl;
    }                  
  
 cin.get(); // and here?
}

[coderitr]

Because when you run a console application from Windows, it is configured to close the console when the program has finished. The last cin.get() keeps the program from ending and thereby leaves the window open. If you open a command prompt and run the program from the command line you'll see the same result only it is manifest by the console returning to the entry prompt. You can leave the last cin.get() in place but I would suggest displaying something like "press any key to continue" so the user knows what to do at that point. You should not need the cin.get() at the top of the program at all.

Welcome to TSG.

[coderitr]

Okay, admittedly I don't fully understand the iostream objects in C++ but when I removed the first cin.get( ) from your code and ran it, it didn't stop on the last one but just returned to the C: prompt. The only possible explanation that I can give is that there is something in the keyboard buffer that the last cin.get() "gets" and with the first one on place, it is gone so the second one suspends the program exit.

[Shadow2531]

I usually use cin.ignore() instead of system("pause") in cstdlib , but just like cin.get() , cin.ignore() will have to be done twice unless you clear the buffer with fflush(stdin); in cstdio.

The ideal way would be to use

string input;
getline(cin,input);

, validate it as a string, tokenize based on the operators, do the necessary conversion to float and then computer the value.

It's more code, but if done right, you can input whatever you want, like

4 + 77 + 1056 - 22 / 3

Order of operation, parenthesis and brackets would have to be considered.

Just pointing out that I myself avoid cin like the plague.