while loop validation

[kunz]

Is there a simpler way to write

	//Validating input to R,S,P and Q
while (my_choice != 'R' && my_choice != 'P' && my_choice != 'S' && my_choice != 'Q')//is there a simpler way to write this 
		{
				
				cout << "\nInvalid option. Please Try Again.\n"; 
				cout << "\nMake your choice [R,P,S]. Enter Q to Quit. ";
				cin  >> user_choice;//promotes user to enter a choice 
		
		}
return my_choice;

[minomic]

Since the letters are in sequence (P, Q, R, S) you can use something related to the ASCII code:

while (my_choice < 'P' || my_choice > 'S') {
    // invalid
}

Otherwise you can just put your validation code in a separate method:

bool validate_option (char my_option) {
    ...
}

[kunz]

isnt there any thing easier like

char my_choice;
while (!(my_choice=R ...) //i dont know how to go about it can some one help please  

[minomic]

Well it's just the same thing but applying De Morgan's rules:

while(!(my_choice == 'R' || my_choice == 'P' || ...))

but it doesn't seem to be easier...

Don't you like the little trick with the ASCII code? According to me, that's the easiest way.

[Momothegreat]

Simpler ways?
It's just different logical equivalencies.
And minomic's original suggestion does seem to be fairly simple.

[andywestken]

Not sure this is simpler...

And it's prob. overkill for just 4 options.

... but using string::find() does scale better.

Andy

#include <iostream>
#include <string>
using namespace std;

char getChoice();

int main () {
    cout << "Your choice?\n";

    char choice = getChoice();

    cout << "Got choice \'" << choice << "\'\n";

    return 0;
}

// Validating input to R,S,P and Q
char getChoice() {
    char my_choice = '?'; // init to something else 
    const string options = "RSPQ";
    while (options.npos == options.find(my_choice))
    {
        cout << "\nInvalid option. Please Try Again.\n";
        cout << "\nMake your choice [R,P,S]. Enter Q to Quit. ";
        cin  >> my_choice; //promotes user to enter a choice (was user_choice)
    }
    return my_choice;
}

Note that in C code you can do a similar kind of thing using strstr() strchr()
Edit: yes, I "meant" strchr when I wrote strstr...

[dhayden]

andywestken's solution is a very handy trick to remember. For efficiency, it's important to make the string const (or static).

Note that in C code you can do a similar kind of thing using strstr()

I think you meant strchr():

if (strchr("RSPQ", my_choice) == nullptr) {
    cout << "invalid input\n";
}