Why does program skip over for loop with string arrays and cin/cout

Question

My goal was to make the program as efficient as possible. I have been stuck on this problem for quite some time and when I searched it up I was told to flush/endl the cout statements.

When I began debugging I deduced it was the for loops that were the issue. It would just skip over the for loop, resulting in length, width, height being 0.

#include <iostream>
#include <string>
#include <array>
using std::cout;    using std::cin;
using std::string;   using std::flush;
using std::endl;

void main()
{
    int length=0, width=0, height=0, volume=0;
    int VolCalcs[3]={length, width, height};

    string Prompt[3] = {"Please enter length: ", "Please enter width: ", "Please enter height: "};
    string NewResult[3] = {"The new length is ", "The new width is ", "The new height is "};

    for(int i=0;i==3;++i)
    {
        cout<<endl;
        cout<<Prompt[i]<<flush;
        cin>>VolCalcs[i];
    }

    volume=length*width*height;
    cout<<" The Volume is: "<<volume<<endl;

    length++;
    width--;
    height+=10;


    for(int i=0;i==3;++i)
    {
        cout<<NewResult[i] << VolCalcs[i] <<endl;
    }
    volume=length*width*height;
    cout<<" The New Volume is: "<<volume<<endl<<endl;
    cout<<"Press Enter to End Program"<<flush;
    cin.ignore();
}

The output is as follows:

The Volume is: 0

The New Volume is: -10

Press Enter to End Program

Your code is very confused, and I'm afraid giving you the fixes for the various mistakes here will not really help you get to grips with C++. I suggest you start over with [a good book](http://stackoverflow.com/q/388242/1171191). And stop listening to whoever tried to explain `endl` and `flush` to you. — BoBTFish, Sep 29 '15 at 13:36
Also, you're setting `VolCalcs` to be copies of `length, width` and `height`, not references to them. So the input operations won't affect `length, width, height`. Your attempts to modify `length`, `width`, and `height` later also aren't reflected in `VolCalcs`, which you output in the second loop. Get rid of the separate `length`, `width` and `height` variables, and just use the `VolCalcs` array everywhere. Fix the loop condition, and you should be closer to a working solution. — Andrew, Sep 29 '15 at 13:38

Lukáš Bednařík · Accepted Answer · 2015-09-29T16:54:43.417

I see the following errors:

The main should always return int.
The for loop condition should be for (int i = 0; i != 3; ++i). Note you need to change both of your for loops. The for loop condition i != 3 means the the loop should continue if i != 3.
You mix the use of an array with the use of variables. There are two options:
- Use variables: Remove VolCalcs and use only plain variables length, width, height. Remove loops.
- Use array. Remove length, width, height and use only array. In the fix below I use length, width, height only for array initialization, but these variables are not used further in the code.

#include <iostream>
#include <string>
#include <array>
using std::cout;    using std::cin;
using std::string;   using std::flush;
using std::endl;
int main()
{
    int length=0, width=0, height=0, volume=0;
    int VolCalcs[3]={length, width, height};
    string Prompt[3] = {"Please enter length: ", "Please enter width: ", "Please enter height: "};
    string NewResult[3] = {"The new length is ", "The new width is ", "The new height is "};

    for (int i=0; i != 3; ++i)
    {
        cout<<endl;
        cout<<Prompt[i]<<flush;
        cin>>VolCalcs[i];
    }

    volume=VolCalcs[0]*VolCalcs[1]*VolCalcs[2];
    cout << " The Volume is: "<<volume<<endl;

    VolCalcs[0]++;
    VolCalcs[1]--;
    VolCalcs[2]+=10;


    for(int i=0;i!=3;++i)
    {
        cout<<NewResult[i] << VolCalcs[i] <<endl;
    }
    volume=VolCalcs[0]*VolCalcs[1]*VolCalcs[2];
    cout<<" The New Volume is: "<<volume<<endl<<endl;
    cout<<"Press Enter to End Program"<<flush;
    cin.ignore();

    return 0;
}

Now let me play with your code a little bit...

#include <iostream>
#include <string>

using namespace std;


int main()
{
    int VolCalcs[3] = {0, 0, 0};
    string Prompt[3] = {"Please enter length: ", "Please enter width: ", "Please enter height: "};
    string NewResult[3] = {"The new length is ", "The new width is ", "The new height is "};

    for (int i=0; i != 3; ++i) {
        cout << endl;
        cout << Prompt[i] << flush;
        cin >> VolCalcs[i];
    }

    int volume = VolCalcs[0] * VolCalcs[1] * VolCalcs[2];
    cout << " The Volume is: " << volume << endl;

    ++VolCalcs[0];
    --VolCalcs[1];
    VolCalcs[2] += 10;

    for (int i = 0; i != 3; ++i) {
        cout << NewResult[i] << VolCalcs[i] << endl;
    }
    volume = VolCalcs[0] * VolCalcs[1] * VolCalcs[2];
    cout << " The New Volume is: " << volume << endl << endl;
    cout << "Press Enter to End Program" << flush;
    cin.ignore();

    return 0;
}

What changed?

Prefer prefix operator ++i to postfix i++. For example in ++VolCalcs[0].
Write spaces around operators. This is a good formatting practice.
Postpone variable definitions as long as possible. Create volume when it is needed.
The #include <array> is not needed. Prefer std::array before plain old C style arrays. They aren't in my code. It's probably your next step :)

Why does program skip over for loop with string arrays and cin/cout

1 Answers1