Question

I have been trying to make a method where the user can input a value between x and y. A while-loop ensures that the input value stays between x and y, and my try-catch is supposed to throw an exception if the user enters an invalid variable (i.e. user enters “e” when the program expects an integer). The do-while loop serves to loop the method as long as a valid variable has not been entered.

here is my code, when i run it everything runs fine except for when i try to enter an invalid variable (for example if i enter ‘e’ or ‘$’), then my program just loops the code “NSLog(@”Enter a number between %i and %i”, min, max)” infinitely.

#import <Foundation/Foundation.h>
@interface UI : NSObject
{
    int a;
    int ok;
}

-(int)getInt:(int)min:(int)max;

@end

@implementation UI

-(int) getInt: (int) min: (int) max{
    ok = 0;

    do {
        @try {
            NSLog(@"Enter a number between %i and %i: ", min, max);
            scanf("%i", &a);
            while(a<min || a>max){
                NSLog(@"Make sure your number is between %i and %i: ", min, max);
                scanf("%i", &a);
            }
            ok=1;

        }
        @catch (NSException * e) {
            NSLog(@"Error. Re-enter your number");
        }
    } while (ok=0);

    return a;
}

@end




int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    UI *ui = [[UI alloc] init];

    NSLog(@"The number you entered is %i", [ui getInt:1 :10]);

    [ui release];
    [pool drain];
    return 0;
}

Answer 1

You don’t actually have any code there that throws an exception, so it’s not surprising that no exception is being thrown. To throw an exception you would use @throw.

However, this isn’t how you should do this anyway. Exceptions in Objective-C are nearly always reserved for non-recoverable programming errors, not incorrect user input. You should not use exceptions for normal control flow.