Help with validating user input

[mollywhoppinRBG]

I am doing a problem from my book I think I have everything else right
except I can't seem to figure out how the validate choices. Help would be greatly appreciated.

(directions from the book ) Input validation: Display an error message if the user enters a number outside the range of 1 through 4 when selecting an item from the menu. Do no accept negative values for the circle radius, the rectangle's length or width, or the triangle's base or height.

#include <iostream>
#include <string>
#include <iomanip>
#include <cstdlib>
#include <ctime>
#include <cmath>

using namespace std;

int main()
{int choice ;// To hold menu choices
  
 const int choiceA = 1,// Constant choic3 value answers 1-4
		   choiceB = 2,
	       choiceC = 3,
	       choiceD = 4;
	
 

 
 // dislay the directions and intent of the program
 cout << " This program is a simple geometry calculator that will compute\n";
 cout << " the area of circle, rectangle, and triangle.\n";
 cout << " please select on of the following choices 1-4\n";
 cout << " any other other inputs besides 1-4 will cause the program to stop.\n\n";
 
 cout << " 1. To calculate Area of circle:\n";// The menu print out the choices
 cout << " 2. To calculate Area of rectangle:\n";
 cout << " 3. To calculate Area of triangle:\n";
 cout << " 4. To quit:\n\n\n";

 cout << " What is your choice ?\n\n";
 cin >> choice;

	if (choice == choiceA)// The if / else for cirlce area
	{
	
		const double PI = 3.14159;// const for pi
		double circleArea;// variable to hold cirlce area equation
		double radius;// user input variable

		cout << " Enter the radius :\n";
		cin >> radius;
		circleArea = PI * pow(radius, 2.0);// to do radius to the snd power this is needed
		cout << " The area of a circle is " << setprecision(5)  << circleArea << "." << endl;
		
	}
	
	
		else if (choice == choiceB)// Display the output and choices #2
		{
				double lenght;//Variables for the lenght, width, and output
				double width;
				double recOutput;
				cout << " Enter the lenght of rectangle: ";
				cin >> lenght;
				cout << " Enter the width of rectangle: ";
				cin >> width;
				recOutput = lenght * width;
				cout << " The area of the rectangle is " << setprecision(7) << showpoint << recOutput << " .\n";


		}

	else if ( choice == choiceC)//For the triangle
	{
		double triBase;//Variables for triangle base, height, output
		double triHeight;
		double triOutput;
		const double triangleopp = .5;// constant variable to hole opperand .5

		cout << " Enter the Base: ";
		cin >> triBase;
		cout << " Enter the Height: ";
		cin >> triHeight;
		triOutput = triangleopp * triBase * triHeight;
		cout << "The area of the triangle is " << setprecision(7) << showpoint << triOutput << ".\n";
	}

		else if (choice == choiceD)// the quit option
		{
		string optionQuit;
			cout << " Do you wan to quit the program? ";
			cin >> optionQuit;
			cout << " The program will now quit\n";
		}





}

[Handy Andy]

Hello mollywhoppinRBG,

This with the comments in the code is as far as I have reached:

#include <iostream>
#include <string>
#include <iomanip>
#include <cstdlib>
#include <ctime>
#include <cmath>

//using namespace std;  // <--- Best not to use.
// The most recent post that is worth reading. http://www.cplusplus.com/forum/beginner/258335/

// <--- A better option.
using std::cin;
using std::cout;
using std::endl;
using std::fixed;
using std::showpoint;
using std::setprecision;
using std::string;

int main()
{
	int choice;// To hold menu choices

	const int choiceA = 1,// Constant choic3 value answers 1-4
		choiceB = 2,
		choiceC = 3,
		choiceD = 4;

	// dislay the directions and intent of the program
	cout << " This program is a simple geometry calculator that will compute\n";
	cout << " the area of circle, rectangle, and triangle.\n";
	cout << " please select on of the following choices 1-4\n";
	cout << " any other other inputs besides 1-4 will cause the program to stop.\n\n";

	// **********************************************************
	//                 NEEED TO VALIDATE INPTU.

	cout << " 1. To calculate Area of circle:\n";// The menu print out the choices
	cout << " 2. To calculate Area of rectangle:\n";
	cout << " 3. To calculate Area of triangle:\n";
	cout << " 4. To quit:\n";  // <--- Changed.
	cout << "  What is your choice ? ";  // <--- Changed.
	cin >> choice;

	//                   Maybe a do/while loop.
	// **********************************************************

	if (choice == choiceA)// The if / else for cirlce area
	{

		const double PI = 3.14159;// const for pi
		double circleArea;// variable to hold cirlce area equation
		double radius;// user input variable

		cout << " Enter the radius :\n";
		cin >> radius;

		// **********************************************************
		//                 NEEED TO VALIDATE INPTU.
		// **********************************************************

		circleArea = PI * pow(radius, 2.0);// to do radius to the snd power this is needed

		cout << " The area of a circle is " << setprecision(5) << circleArea << "." << endl;
	}

	else if (choice == choiceB)// Display the output and choices #2
	{
		double lenght;//Variables for the lenght, width, and output
		double width;
		double recOutput;

		cout << " Enter the lenght of rectangle: ";
		cin >> lenght;

		// **********************************************************
		//                 NEEED TO VALIDATE INPTU.
		// **********************************************************

		cout << " Enter the width of rectangle: ";
		cin >> width;

		// **********************************************************
		//                 NEEED TO VALIDATE INPTU.
		// **********************************************************

		recOutput = lenght * width;

		cout << " The area of the rectangle is " << setprecision(7) << showpoint << recOutput << " .\n";
	}

	else if (choice == choiceC)//For the triangle
	{
		const double triangleopp = .5;// constant variable to hole opperand .5

		double triBase;//Variables for triangle base, height, output
		double triHeight;
		double triOutput;

		cout << " Enter the Base: ";
		cin >> triBase;

		// **********************************************************
		//                 NEEED TO VALIDATE INPTU.
		// **********************************************************

		cout << " Enter the Height: ";
		cin >> triHeight;

		triOutput = triangleopp * triBase * triHeight;

		cout << "The area of the triangle is " << setprecision(7) << showpoint << triOutput << ".\n";
	}

	else if (choice == choiceD)// the quit option
	{
		string optionQuit;

		cout << " Do you wan to quit the program? ";
		cin >> optionQuit;

		cout << " The program will now quit\n";
	}
}

What you would do for lines 38 - 43 would need to be done for the other inputs. If you are having a problem with this just say so.

Andy

Edit:

P.S. watch your indenting and use of {}s. Be consistent with their use.

[Handy Andy]

Hello mollywhoppinRBG,

There are several ways to validate what you need. Also you need to consider what needs checked.

This is just one example of what you could do:

int main()
{
	int choice;// To hold menu choices

	const int // Constant choic3 value answers 1-4
		choiceA = 1,
		choiceB = 2,
		choiceC = 3,
		choiceD = 4;

	// dislay the directions and intent of the program
	cout  // <--- An alternative way of writing this.
		<< " This program is a simple geometry calculator that will compute\n"
		<< " the area of circle, rectangle, and triangle.\n"
		<< " please select on of the following choices 1-4\n" << " any other other"
		<< "inputs besides 1-4 will cause the program to stop.\n"  // <--- 2 "\n"s should work and flush the output buffer.
                << std::endl;  // <--- Or save the "endl" for after the last line.

	// **********************************************************
	//                 NEED TO VALIDATE INPUT.

	do
	{
		cout << " 1. To calculate Area of circle:\n";// The menu print out the choices
		cout << " 2. To calculate Area of rectangle:\n";
		cout << " 3. To calculate Area of triangle:\n";
		cout << " 4. To quit:\n";  // <--- Changed.
		cout << "  What is your choice ? ";  // <--- Changed.
		cin >> choice;

		if(!cin || choice < 1 || choice > 4)
		{ 
			if (!cin)
			{
				std::cout << "\n    Invalid input! Your choice must be a number between (1 and 4)\n\n";

				std::cin.clear();
				std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');  // <--- Requires header file <limits>.
			}
			else if (choice < 1 || choice > 4)
			{
				std::cout << "\n    Invalid choice! Your choice must be a number between (1 and 4)\n\n";
			}
		}
	} while (choice < 1 || choice > 4);
	//                   Maybe a do/while loop.
	// ********************************************************** 

Just an idea to get you started.

Andy