Need help not allowing a negative number to be input
 

I do not want a negative number input for radius, length, width, base, height. How would I do this. My code is below. It should be pretty self explanatory.

Thanks.

[CODE]

#include <iostream>

#include <cmath>





using namespace std;



int main ()



{

                double const pi=3.14159;

                int radius,

                        length,

                        width,

                        base,

                        height,

                        choice;

                double        area;

                

                



        //Display the menu and get the user's choice

                cout << "         Geometry Calculator \n\n";

                cout << "1. Calculate the Area of a Circle\n";

                cout << "2. Calculate the Area of a Rectangle\n";

                cout << "3. Calculate the Area of a Trainge\n";

                cout << "4. Quit\n";

                cout << "\n";



                cout <<"Enter your choice (1-4): ";

                cin >> choice;

                cout << "\n";



                if (choice==1)

                   {cout << "Please enter the radius of the circle: ";

                        cin >> radius;

                        area = radius * pi;

                        cout << "The area of the circle is: " << area << endl;}



                   else if (choice==2)

                   {cout << "Please enter the length of the rectangle: ";

                        cin >> length;

                        cout << "Please enter the width of the rectangle: ";

                        cin >> width;

                        area = length * width;

                        cout << "The area of the rectangle is: " << area << endl;}

     

                        else if (choice==3)

                        {cout << "Please enter the base length of the triangle: ";

                        cin >> base;

                        cout << "Please enter the height of the triangle: ";

                        cin >> height;

                        area = (base * height)/2;

                        cout << "The area of the triangle is: " << area << endl;}

     

                        else if (choice==4)

                        {cout << "Thanks for trying the Geometry Calculator\n";}



                        else

                        {cout << "You can only select options 1-4, run the program again and select a option 1-4\n"; }

     

     

                return 0;



}

Re: Need help not allowing a negative number to be input
 

Write a function that does not allow for negative input:

int GetNonNegativeInteger ()

{

     int input;

     cin >> input;

     while (input < 0)

     {

          // display error message.

          // ask for input again

     }



     return input;

}

Call this function from main when you need non-negative integer input.

Re: Need help not allowing a negative number to be input
 

Now I am confused.

Re: Need help not allowing a negative number to be input
 

Where should the function go or where should the function call go?

Re: Need help not allowing a negative number to be input
 

With what you did what part of my code would I add that in. I am just not getting it. I do not have any variable called input. I am lost.

Re: Need help not allowing a negative number to be input
 

Ok I got it. Here is my new code

[CODE]

#include <iostream>

#include <cmath>





using namespace std;





int main ()



{

                double const pi=3.14159;

                int radius,

                        length,

                        width,

                        base,

                        height,

                        choice;

                        double        area;

                

                



        //Display the menu and get the user's choice

                cout << "         Geometry Calculator \n\n";

                cout << "1. Calculate the Area of a Circle\n";

                cout << "2. Calculate the Area of a Rectangle\n";

                cout << "3. Calculate the Area of a Trainge\n";

                cout << "4. Quit\n";

                cout << "\n";



                cout <<"Enter your choice (1-4): ";

                cin >> choice;

                cout << "\n";



                                

                   if (choice==1)

                   {cout << "Please enter the radius of the circle: ";

                    cin >> radius;

                        while (radius<0)

                        {cout << "Please enter a positive number: ";

                        cin >> radius;}

                        area = radius * pi;

                        cout << "The area of the circle is: " << area << endl;}



                   else if (choice==2)

                   {cout << "Please enter the length of the rectangle: ";

                        cin >> length;

                        while (length<0)

                        {cout << "Please enter a positive number: ";

                        cin >> length;}

                        cout << "Please enter the width of the rectangle: ";

                        cin >> width;

                        while (width<0)

                        {cout << "Please enter a positive number: ";

                        cin >> width;}

                        area = length * width;

                        cout << "The area of the rectangle is: " << area << endl;}

     

                        else if (choice==3)

                        {cout << "Please enter the base length of the triangle: ";

                        cin >> base;

                        while (base<0)

                        {cout << "Please enter a positive number: ";

                        cin >> base;}

                        cout << "Please enter the height of the triangle: ";

                        cin >> height;

                        while (height<0)

                        {cout << "Please enter a positive number: ";

                        cin >> height;}

                        area = (base * height)/2;

                        cout << "The area of the triangle is: " << area << endl;}

     

                        else if (choice==4)

                        {cout << "Thanks for trying the Geometry Calculator\n";}



                        else

                        {cout << "You can only select options 1-4, run the program again and select a option 1-4\n"; }

     

     

                return 0;



}

Re: Need help not allowing a negative number to be input
 

#include <iostream>

#include <cmath>





using namespace std;







int GetNonNegativeInteger ()

{

     int input;

     cin >> input;

     while (input < 0)

     {

          // display error message.

          // ask for input again

     }



     return input;

}







int main ()



{

                double const pi=3.14159;

                int radius,

                        length,

                        width,

                        base,

                        height,

                        choice;

                double        area;

                

                



        //Display the menu and get the user's choice

                cout << "         Geometry Calculator \n\n";

                cout << "1. Calculate the Area of a Circle\n";

                cout << "2. Calculate the Area of a Rectangle\n";

                cout << "3. Calculate the Area of a Trainge\n";

                cout << "4. Quit\n";

                cout << "\n";



                cout <<"Enter your choice (1-4): ";

                cin >> choice;

                cout << "\n";



                if (choice==1)

                   {cout << "Please enter the radius of the circle: ";

                        radius = GetNonNegativeInteger ();

                        area = radius * pi;

                        cout << "The area of the circle is: " << area << endl;}



                   else if (choice==2)

                   {cout << "Please enter the length of the rectangle: ";

                        length = GetNonNegativeInteger ();

                        cout << "Please enter the width of the rectangle: ";

                        width = GetNonNegativeInteger ();

                        area = length * width;

                        cout << "The area of the rectangle is: " << area << endl;}

     

                        else if (choice==3)

                        {cout << "Please enter the base length of the triangle: ";

                        cin >> base;

                        cout << "Please enter the height of the triangle: ";

                        cin >> height;

                        area = (base * height)/2;

                        cout << "The area of the triangle is: " << area << endl;}

     

                        else if (choice==4)

                        {cout << "Thanks for trying the Geometry Calculator\n";}



                        else

                        {cout << "You can only select options 1-4, run the program again and select a option 1-4\n"; }

     

     

                return 0;



}

See red. You would do the same for base and height in option number 3. Have you used functions before? You need to change the commented parts of the function.

Re: Need help not allowing a negative number to be input
 

Ok here is my final code. Cleaned it up a bit so it would not just say enter a positive number each time a negative number was entered

#include <iostream>

#include <cmath>





using namespace std;





int main ()



{

                double const pi=3.14159;

                int radius,

                        length,

                        width,

                        base,

                        height,

                        choice;

                        double        area;

                

                



        //Display the menu and get the user's choice

                cout << "         Geometry Calculator \n\n";

                cout << "1. Calculate the Area of a Circle\n";

                cout << "2. Calculate the Area of a Rectangle\n";

                cout << "3. Calculate the Area of a Trainge\n";

                cout << "4. Quit\n";

                cout << "\n";



                cout <<"Enter your choice (1-4): ";

                cin >> choice;

                cout << "\n";



                                

                   if (choice==1)

                   {cout << "Please enter the radius of the circle: ";

                    cin >> radius;

                        while (radius<0)

                        {cout << "Negative radius not allowed, enter a positive radius: ";

                        cin >> radius;}

                        area = radius * pi;

                        cout << "The area of the circle is: " << area << endl;}



                   else if (choice==2)

                   {cout << "Please enter the length of the rectangle: ";

                        cin >> length;

                        while (length<0)

                        {cout << "Negative length not allowed, enter a positive length: ";

                        cin >> length;}

                        cout << "Please enter the width of the rectangle: ";

                        cin >> width;

                        while (width<0)

                        {cout << "Negative width not allowed, enter a positive width: ";

                        cin >> width;}

                        area = length * width;

                        cout << "The area of the rectangle is: " << area << endl;}

     

                        else if (choice==3)

                        {cout << "Please enter the base length of the triangle: ";

                        cin >> base;

                        while (base<0)

                        {cout << "Negative base not allowed, enter a positive base: ";

                        cin >> base;}

                        cout << "Please enter the height of the triangle: ";

                        cin >> height;

                        while (height<0)

                        {cout << "Negative height not allowed, enter a positive height: ";

                        cin >> height;}

                        area = (base * height)/2;

                        cout << "The area of the triangle is: " << area << endl;}

     

                        else if (choice==4)

                        {cout << "Thanks for trying the Geometry Calculator\n";}



                        else

                        {cout << "You can only select options 1-4, run the program again and select a option 1-4\n"; }

     

     

                return 0;



}

Re: Need help not allowing a negative number to be input
 

I am very new at this. First time running C++. We have not learned functions yet. What do you mean change the commented parts of the function. I redid some code a little different then what you showed and it works.

Re: Need help not allowing a negative number to be input
 

Yes, you did the same thing as what I was recommending, just you didn't use functions. What I meant by change the commented sections is to do what you did in your code:

int GetNonNegativeInteger ()

{

     int input;

     cin >> input;

     while (input < 0)

     {

          // display error message.

          // ask for input again

     }



     return input;

}

Change the red code to this:

cout << "Negative number not allowed." << endl;

cin >> input;

Which is what you have in your code, just slightly different each time, which is correct. If you are not going to use a function, doing it the way you did it is correct and is equivalent. When you learn functions, you'll probably do it the way I did it since you are doing the same thing five times. You did it right.