switch statement: validating user input

[ajp16]

I'm writing a program that calculates the area of a circle, triangle, rectangle. However, the program is not supposed to accept negative values for radius, length, width, ...etc. I've seen how to do it with if / else statements, but can't figure it out with switch statements. Any help would be appreciated.

#include <iostream>
#include <iomanip>
#incldue <cmath>
using namespace std;

int main()
{
  int radius, length, width, height, base, choice;

  double cirArea  = 0;
         rectArea = 0;
         triArea  = 0;
  const in
         Area_of_Circle    = 1,
         Area_of_Rectangle = 2,
         Area_of_Triangle  = 3,
         Quit              = 4;

  cout << "This program will calculate the area of a circle, rectangle,";
  cout << " or triangle.\n";
  cout << "Please select from the menu choices below.\n";
  cout << "Enter the corresponding number with the calculation";
  cout << " you would like to perform.\n";
  cout << "1. Area of a Circle\n";
  cout << "2. Area of a Rectangle\n";
  cout << "3. Area of a Triangle\n";
  cout << "4. Quit\n";
  cin >> choice;

  switch (choice)
  {
    case 1:  cout << "You chose 1 to find the area of a circle.\n";
             cout << "Please enter the radius of the circle.\n";
             cin >> radius;
             cirArea = 3.14159 * (radius * radius)
             cout << "The are of the circle is " << cirArea << "." << endl;
    break;

Then the code continues on the same way for the other menu options, with a default statement that throws out an error message if the user enters any other number other 1-4 for the menu options. Again, any help would be appreciated. Thanks

[TarikNeaj]

Hey, please always put your code between code tags <> under the format section - http://www.cplusplus.com/articles/jEywvCM9/


You can have if statements inside the cases.

case 1: cout << "You chose 1 to find the area of a circle.\n";
cout << "Please enter the radius of the circle.\n";
cin >> radius;

if(radius < 0)
{
     cout << "No can do!" << endl;
}

etc.. you'd need a loop aswell ofc. but you get the point I hope.

[dhayden]

Unless you us a break statement, the program control flows from one case right into then next. So you almost always need a break; after each case:

switch (choice) {
case 1:
    cout << "Please enter the radius of the circle.\n";
    cin >> radius;
    cirArea = 3.14159 * (radius * radius)
    cout << "The are of the circle is " << cirArea << "." << endl;
    break;
case 2:
    // code to do a rectangle
    break;
case 3:
    // code to do a triangle
    break;
case 4:
    quit = true;
    break;
default:
    // code to tell user the input is invalid
    break;
}

Some good habits to follow when writing switch statements:
- If the code should not flow from one case into the next one, then use a break statement, even with the last case in the statement (such as the default one above). This way if you change the order or add a new case, the code will still work.
- If the code should flow from one case into the next, then put a comment at the end of the first case stating that you're doing in deliberately. I use // fallthrough .

[ajp16]

problem solved. Thanks guys! sorry about that with the code tags..... first post.