Thread: C++ programing , Loops , infinite loops issue

Hi,
I am new to this forum, so please don't be mean to me if I didn't know what to say or what to write or not.

My Problem starts with the idea of creating a calculator
and I tried to do that using everything I learn so far (I'm still a beginner)
and I ended up with this code that worked perfectly in the beginning until I decided to test it and I found this infinite loops issue
this is the code

Code:

#include <iostream>

using namespace std;


double add(double x,double y);
double subtract(double x,double y);
double multiply(double x,double y);
double divide(double x,double y);


int main()
{
    int i = 0;
    while( i == 0 )
    {
       double x, y;
       char op;


       cin >> x;  //the first argument to the numerical operation
       cin >> op; //The numerical operation indicator
       cin >> y;  //The second argument to the numerical operation


       /*
       we are going to use four condition because we know four numerical operations +,-,*,/.
       */

       if(op == '+')
        {
            cout<< "= " << add(x,y) << endl;
            continue;
        }
      else if(op == '-')
        {
            cout<< "= " << subtract(x,y) << endl;
            continue;
        }
       else if(op == '*')
        {
            cout << "= " << multiply(x,y) << endl;
            continue;
        }
       else if(op == '/')
        {
            cout << "= " << divide(x,y) << endl;
            continue;
        }
        else
        {
            ++i;
        }
    }
}




double add(double x,double y)
{
    return x + y;
}


double subtract(double x,double y)
{
    return x - y;
}


double multiply(double x,double y)
{
    return x * y;
}


double divide(double x,double y)
{
    return x / y;
}

the problem is
when I enter a character from the start other than +,-,*,/ the programs stops and that what i want
But when i do this
Attachment 13583
Attachment 13584
Attachment 13585

Please i need your help with this , i tried all the fixes i could think of but none of them solved the problem

What exactly is this "infinite loop issue"?

Why do you need the variable named i?

As for the issue: you should check that the input was successful, e.g.,

Code:

if (cin >> x >> op >> y)

Originally Posted by Ibrahim Lawleit

i used the i variable so that if the variable op didn't meet any of the conditions it will result in ++i which will force the condition to change and become false because i is not equal to 0 any more

Use a bool variable instead.

What is your current code?

>>if(!( cin>>x>>op>>y ) )
This statement reads into x, op and y. So you are essentially doing it twice.
The idea is that when you first read into x, op and y, you need to check if it worked or not and then take appropriate measures.

It might also help if you gave a sample of the input you're supplying that causes your code to demonstrate the concern.

>>cin >> x >> op >> y
This means first read a double into x, then read one character, then read one double into y.
Each operation (cin >> var) returns the stream itself, allowing you to chain operations.

So the result of (cin >> x) is std::cin itself.
Now, that means that (cin >> x >> op >> y) return std::cin itself.
If for some the operator >> fails (i.e. fail to read some input), then the input stream goes into an error state. You can check if the stream if still in a good condition by using an if statement, like if (std::cin).
If this checks fails, it means a read failed, so you can do an appropriate action.