Need help not allowing a negative number to be input

[davids2004]

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=syntax]
#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;

}

[VernonDozier]

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.

[davids2004]

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.

Now I am confused.

[VernonDozier]

Where should this go in my code?

Thanks.

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

[davids2004]

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

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.

[davids2004]

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

Ok I got it. Here is my new code

[code=syntax]#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;

}

[VernonDozier]

#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.

[davids2004]

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;

}

[davids2004]

#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.

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.

[VernonDozier]

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.

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.

[davids2004]

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.

Thanks for your help. I gave you rep as well.