[RESOLVED] Integer based console menu problem

[lkallas]

Hi!

I have a problem with a integer based menu that I use in my console program.

#include <string>
#include <iostream>

using namespace std;



int menu()
{
	int choice = 0;


	do {
		cout << "\nMenu\n" << endl;
		cout << "[1] Do something." << endl;
		cout << "[2] Do something else." << endl;
		cout << "[3] Do something entirely different." << endl;
		cout << "[4] Quit." << endl;
		cout << "Your choice: ";

		choice = 0;
		
		if (!(cin >> choice) || (choice < 1) || (choice > 4)) {
			cout << "Invalid choice! \nChoice needs to be in range 1 to 4" << endl;
			cin.clear();
			cin.ignore(1000, '\n');
		}
	} while (choice < 1 || choice > 4);
	
	return choice;
}


int main()
{
	int choice = 0;

	do {

		switch (choice = menu()) {
		case 1:
			cout << "You chose 1!" << endl;
			//Do something
			break;
		case 2:
			cout << "You chose 2!" << endl;
			//Do something
			break;

		case 3:
			cout << "You chose 3!" << endl;
			//Do something
			break;


		case 4:
			/* Quit program */
			break;

		default:
			/* Just for testing. This is not supposed to happen in runtime. */
			cout << "Oops! Something went wrong!" << endl;

		}
	} while (choice != 4);

	return 0;
}

Now when I input single integer it works fine. But when I insert something like "1 2 3 4" it loops all the numbers and the result is:

Menu

[1] Do something.
[2] Do something else.
[3] Do something entirely different.
[4] Quit.
Your choice: 1 2 3 4
You chose 1!

Menu

[1] Do something.
[2] Do something else.
[3] Do something entirely different.
[4] Quit.
Your choice: You chose 2!

Menu

[1] Do something.
[2] Do something else.
[3] Do something entirely different.
[4] Quit.
Your choice: You chose 3!

Menu

[1] Do something.
[2] Do something else.
[3] Do something entirely different.
[4] Quit.
Your choice:
--------------------------------
Process exited after 3.484 seconds with return value 0
Press any key to continue . . .

"1 2 3 4" is invalid input and needs to be handled. Any idea how to handle this situation?

[2kaud]

For the input 1 2 3 4, the stream extraction operator >> will first get the 1 leaving 2 3 4 in the stream. As this is a valid input menu() returns. The next time menu() is called the input stream still contains 2 3 4 so >> extracts 2 and continues. This repeats until either the stream is empty in which case >> will wiat until further input has been entered or an invalid number is found. Try changing

	return choice;

to

	cin.ignore(1000, '\n');
	return choice;

This should remove any remaining chars from the buffer once the first valid entry has been used.

[lkallas]

Thank you 2kaud, good explanation!

cin.ignore(1000, '\n');
return choice;

Does the trick!
But I am wondering if this cin.ignore(1000, '\n'); "hack" is a good way in terms of integer validation. Still "1 2 3 4" is invalid input.

I was thinking something like converting input to string, check the length of the string for example" if (string.length == 1)", check if string[0] is integer and then return true or false.
Is this idea any good? Maybe there is some better practice to achieve what I'm after?

[2kaud]

If you want to count 1 2 3 4 as invalid input rather than 4 inputs of 1 then 2 then 3 then 4 then you need to read the whole line and validate. Something like this

string trim(const string& st)
{
size_t f = st.find_first_not_of(' ');
size_t l = st.find_last_not_of(' ');

	return (f != string::npos && l != string::npos) ? st.substr(f, l - f + 1) : "";
}

int menu()
{
const int max = 4;

int choice = 0;

	do {
		cout << "\nMenu\n" << endl;
		cout << "[1] Do something." << endl;
		cout << "[2] Do something else." << endl;
		cout << "[3] Do something entirely different." << endl;
		cout << "[4] Quit." << endl;
		cout << "Your choice: ";

		string line, tlin;

		if (!getline(cin, line))
			cin.clear();
		else
			tlin = trim(line);

		const char* last = tlin.c_str() + tlin.length();
		char *end;

		choice = strtol(tlin.c_str(), &end, 10);
		if (end != last || choice < 1 || choice > max) {
			cout << "Invalid choice\n";
			choice = 0;
		}

	} while (choice == 0);

	return choice;
}

[lkallas]

And you've made my day again, 2kaud!

The code you've provided is exactly what I was looking for!

Thread resolved!