One of my variables in my simple calculator says that it is not being initialized. Why?

Question

I am a noob to C++, and as a part of homework I had to create a simple calculator with four functions within C++. I have done this and it works, however, I am now trying to loop it so that a user can have infinite attempts at using it, however, I am having struggles. Basically, when I run my program and tell the program which operation I'd like to use, it tells me that my variable "sum" is not being initialized. Im not quite sure what this is, or how to fix it. Any ideas? Here is my code -

#include "stdafx.h"
#include <iostream>
using namespace std;
int main() 
{

    while (true)
    {
        int num1, num2, r;
        double sum;

        cout << "Enter a number\n";
        cin >> num1;

        cout << "Enter another number\n";
        cin >> num2;

        cout << "Please enter an operator (+ , * , /, - or End)\n";
        cin >> r;
        if (r == 'End') break;
        if (r == '+') sum = num1 + num2;
        if (r == '-') sum = num1 - num2;
        if (r == '*') sum = num1 * num2;
        if (r == '/') sum = num1 / num2;

        cout << r;
        cout << "The answer is \n" << sum << endl;
        system("pause");
        return 0;
    }
}

What will be the value of `sum` if the user enters something else than the 5 options you test for? :) — Dan Mašek, Oct 09 '16 at 17:51
Reading into an `int` and expecting formatting ASCII input is wrong, as is expecting `'End'` to be a valid character. — Lightness Races in Orbit, Oct 09 '16 at 18:02

score 1 · Answer 1 · answered Oct 09 '16 at 17:51

1

If the user enters 'a' as operator for example (something else than the valid choices), sum is never assigned a value, but sum is printed.

answered Oct 09 '16 at 17:51

alain

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so what exactly do I need to do ? Im completely noob at C++. – xKetjow Oct 09 '16 at 18:04
1

Which book are you using, @xKetjow? Surely it explains this? – Lightness Races in Orbit Oct 09 '16 at 18:05
im not doing any books, it's one of my units in college, software design and development. we get taught the theory behind programming etc, but not actual programming. – xKetjow Oct 09 '16 at 18:07
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@xKetjow: Learn from a book. http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list – Lightness Races in Orbit Oct 09 '16 at 18:07

Rakete1111 · Answer 2 · 2016-10-09T18:14:06.057

0

The compiler says that you are trying to use an unintialized variable, sum.

If you think you initialize it, think again: You only assign a value if r is +, -, * or /. But what if r is a? _{'End' is not a character, and thus invalid}

Then sum is never initialized/has a value, and so the compiler complains.

edited Oct 09 '16 at 18:14

answered Oct 09 '16 at 17:51

Rakete1111

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In none of those cases is `sum` initialised. Only assigned to. – Lightness Races in Orbit Oct 09 '16 at 18:02
yeah I get that, what exactly do I put into my code for this ? – xKetjow Oct 09 '16 at 18:06
@Light Even if the variable was never initialized in the first place? I always thought that, thanks :) – Rakete1111 Oct 09 '16 at 18:14
2

@Rakete1111: I _think_ old C "street talk" used "initialised" the way you did, but that's not the way the C++ standard or modern C++ "street talk" uses it. – Lightness Races in Orbit Oct 09 '16 at 18:16

score 0 · Answer 3 · answered Oct 09 '16 at 18:07

0

As others have said, the variable sum remains uninitialized if the user enters an invalid choice for r. Just set double sum=0; and you're good to go.

In addition, 'End' is not a char, so you can't compare it to r. You'll have to use some other option for ending.

answered Oct 09 '16 at 18:07

Bikramjeet Singh

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True. It should be a char – Bikramjeet Singh Oct 09 '16 at 18:09
I did the double sum=0 thing and it got rid of that problem :> What should be a char ? – xKetjow Oct 09 '16 at 18:11
Variable r should be a char, not an int. And change 'End' to a single character, say, 'E' – Bikramjeet Singh Oct 09 '16 at 18:16
So i changed it, and it works. When I press E it closes so all gud. One more thing, im not sure how to loop it so that the user can enter more than one equation without having to close the program over and over. I have a loop in there, but it doesnt seem to work. – xKetjow Oct 09 '16 at 18:24
Your loop doesn't work because you've put return 0 within the body of the loop. Shift it outside to just before the last curly brace } and the loop should work. – Bikramjeet Singh Oct 09 '16 at 18:29

One of my variables in my simple calculator says that it is not being initialized. Why?

3 Answers3