User input verification.

[Snaef98]

I was wondering how do i put a system in place to verify user input and block the incorrect input for switch's. For example:

Options are 1-5.

How do i restrict anything less then 1 greater then 5, or characters?
Also how do i ensure the default continues to force a reloop of the switch until the correct input has been entered using cin >>

[hamsterman]

example:

#include <iostream>
#include <limits>

int main(){
    bool valid = false;
    int input;
    while(!valid){
        if(std::cin>>input){//this checks whether an integer was entered
            if(input < 6 && input > 0) valid = true;//then we have to see if this integer is in range
        }else std::cin.clear();//some cleaning up
		
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');//empty input stream

        if(!valid) std::cout << "this input is not valid\n";
    }
    std::cout << input << " is between 1 and 5\n";
    std::cin.get();
    return 0;
}

[Snaef98]

could you recode that using namespace std as thats what im used to.

So in each function i declare

bool valid = false;
int input =0;


where does my switch go within that code, or does it go below that?

[hamsterman]

could you recode that using namespace std as thats what im used to.

What difference does it make?

So in each function i declare...

int input would be there anyway, bool valid could be replaced with a break on line 9, but I think using bools is more clear.

where does my switch go within that code, or does it go below that?

Yes.

[Snaef98]

Well i tried this and it doesn't work it works fine as a stand alone but as soon as i put it into my code it just gives me lots of errors about not being enough parameters and illegal use if ( etc

[Snaef98]

My menus are mostly switchs


Errors:

gdom Of Mythos Revised.cpp(10084) : warning C4003: not enough actual parameters for macro 'max'
1>.\Kingdom Of Mythos Revised.cpp(10084) : error C2589: '(' : illegal token on right side of '::'
1>.\Kingdom Of Mythos Revised.cpp(10084) : error C2143: syntax error : missing ')' before '::'
1>.\Kingdom Of Mythos Revised.cpp(10084) : error C2059: syntax error : ')'

[Snaef98]

This is what i was looking for

cout << "Please make a selection.\n\n<1 = Start Game> <2 = Exit Program>\n";
START:	
	cin >> StartProgram;
	if (cin.fail())
	{
		cin.clear();
		cin.ignore();
		cout << "Incorrect input. Please try again.\n";
		cout << "Please re-enter selection. <1-2>\n";
		goto START;
	}
	else
	{
	switch (StartProgram)
	{
	case 1:  cout << "Now entering game...\n";
			 MainMenu();
			 break;
	case 2:  cout << "\n";
			 break;
	
	default: cout << "Incorrect Selection\n";
			 cout << "Please re-enter selection. <1-2>";
		 	 goto START;
			 break;
	}
	}

If a user enters anything other then 1 or 2, it goes to default and sends them back to the top. If they enter an incorrect input type CHAR it also sends them back and clears input. and this is a good example of when a goto has a good use. Its only for the switch its not going to random parts of a program where you could get confused as to the order of things.

[Duthomhas]

No, it is not a good example of a goto; a simple loop would do just as well. Also, your error handling is needlessly separated into two sections when one would suffice. It is a good start, and excepting your assertion on the use of unconditional jumps, you only need a few tweeks.

For input handling, some modularity is helpful. Here is a complete example to help.

#include <ciso646>
#include <iostream>
#include <limits>
using namespace std;

//----------------------------------------------------------------------------
// This function modularizes the concept of the main menu. It:
//  - displays the menu
//  - gets and validates input
//  - returns a valid menu choice
int main_menu()
  {
  int result = 0;
  cout << "\nMain Menu:\n";
  while (true)
    {
    // Display the menu
    cout << "1 Do something\n"
            "2 Do another thing\n"
            "3 Stop doing things\n"
            "> "
         << flush;

    // Get input.
    // Since our input method does not account for things like "4xy",
    // we'll just clear any extraneous junk from the end of the line.
    // For a more robust input method, see:
    //   http://www.cplusplus.com/forum/beginner/13044/page1.html#msg62827
    cin >> result;

    // Validate the input as (beginning with) an integer in [1,3].
    if ((!cin)
    or  (result < 1)
    or  (result > 3))
      {
      cin.clear();
      cin.ignore( numeric_limits <streamsize> ::max(), '\n' );
      cout << "\n"
              "Hey, that's not a valid input!\n"
              "Please try again:\n";
      }

    // Return a (guaranteed) valid menu choice
    else
      {
      cin.ignore( numeric_limits <streamsize> ::max(), '\n' );
      break;
      }
    }
  return result;
  }

//----------------------------------------------------------------------------
// The main program here is not encumbered with the menu code.
// All it need do is use the above function to get a guaranteed-valid input,
// and act on the result.
// Simple enough.
int main()
  {
  bool done = false;
  cout << "Hello there. Welcome to something simple!\n";
  while (!done)
    {
    switch (main_menu())
      {
      case 1: cout << "\n3 + 3 = " << (3 + 3) << ".\n"; break;
      case 2: cout << "\nNo.\n";                        break;
      case 3: done = true;                              break;
      }
    }
  cout << "\nGood-bye, then.\n";
  return 0;
  }

Hope this helps.