converting char to int in while loop

Question

I am developing a calculator program in c++. But the problem is when I try to convert the character into integer it shows runtime error. The code is given below.

#include<iostream.h>
#include<conio.h>

void main()
{
   clrscr();
   int num,sum=0;
   cout<<"Enter the number"<<endl;
   cin>>num;
   while(num!='=')
   {
      sum=sum+num;
      cin>>num;
   }
   cout<<"The sum is"<<endl;
   getch();
}

The program runs well i.e it takes the input correctly but when I used to press '=' sign then it shows nothing but only the black screen. Please help me. Thankyou.

Does that even compile? You are using <iostream.h> instead of <iostream>. You are using cin, cout, and endl without using the std namespace. — R Sahu
– R Sahu, Commented Aug 4, 2015 at 6:34
You appear to be learning 1980s C++. This is not going to help you whatsoever in the job market. — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Aug 4, 2015 at 12:02

Community · Accepted Answer · 2017-05-23 12:15:42Z

0

After you type '=', this character be convert to int since you declare num as int. But unfortunately the result isn't as you expected. The conversion failed!When an error occurs when reading from a stream, an error flag gets set and no more reading is possible until you clear the error flags. That's why you get an hang

Please refer to cin for an int inputing a char causes Loop that is supposed to check input to go wild

edited May 23, 2017 at 12:15

CommunityBot

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answered Aug 4, 2015 at 7:07

Dean Song

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Comments

Nishant · Accepted Answer · 2015-08-04 07:08:19Z

0

Your issue lies in this loop

while(num!='=')
   {
      sum=sum+num;
      cin>>num;
   }

I will tell you why your code is hanging and why is not asking for more inputs, even if the condition in while loop fails. This happens when you insert a char instead of an int to something, when you input '=' the stream gets corrupted.

You need to use something like this to avoid hanging.

    {
        sum = sum + num;
        cin >> num;
        cin.clear();
        cin.ignore();
    }

And don't insert a char when your code is expecting an int, it sets the error flag and no more reading is possible. And since you can't input char inplace of an int, ask the user at the start how many numbers he wants to add, and then run your loop for that many times to get the input.

like this:

cout<<"Enter the number of items"<<endl;
cin>>items;
cout<<"Enter first item" <<endl;
while(items)
{
cin>>num;
sum=sum+num;
items--;
}

edited Aug 4, 2015 at 7:08

answered Aug 4, 2015 at 6:38

Nishant

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9 Comments

indranil Over a year ago

Thanx for ur rply.. But i also try to put 0x3D instead of '=' but its showing the same problem. y?

Nishant Over a year ago

i already mentioned, once you try to insert char instead of an int inside int type of variable, the error flag is raised and cin stops taking further more input, so at the moment you enter "=", your num variable is not assigned any new value, instead it is storing the old value only.

indranil Over a year ago

Then y Mr R.Sahu is saying to use namespace std ..? and miss ridimha also saying that it will run in turbo C++. ?

Nishant Over a year ago

R.Sahu is right, because <iostream> is standard header for C++, not <iostream.h> Check this stackoverflow.com/questions/2976477/…

Nishant Over a year ago

and cout and cin are global object defined in the std namespace, and endl is a (stream manipulator) function also defined in the std namespace. So you need to use "std" namespace in your code. After including header files, you need to write "using namespace std" in your file... Refer this stackoverflow.com/questions/15346944/…

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