如何使用NSArray和NSDictionary？

Question

I'm learning iOS from iTunes U and trying to build a programmable calculator. I have added three variables which the user can use to allot values. I understand that the variables would be passed as NSString objects and then the user would touch the numbers which would be passed as NSNumbers and allotted to the variables. I don't understand how to use NSArrays and NSDictionary to allot the numbers to these variables. Sorry for being a complete newbie, but I am not comfortable with the Documentation right now, so it is kind of fuzzy! This is my code for appending digits on a UILabel and then using it for calculations:

- (IBAction)digitPressed:(UIButton *)sender {
  NSString *digit = [sender currentTitle];
  if (self.userIsInTheMiddleOfEnteringANumber) {
    self.display.text = [self.display.text stringByAppendingFormat:digit];
    everythingBrainLabel.text = [self.everythingBrainLabel.text stringByAppendingFormat:digit];
  } else {
    self.display.text = digit;
    self.everythingBrainLabel.text = [self.everythingBrainLabel.text stringByAppendingFormat:@" %@", digit];
    self.userIsInTheMiddleOfEnteringANumber = YES;
  }  
}

I can get the values of the variables in an NSMutableArray but how to allot numbers here by simply pressing the digits after pressing the variable? I added NSLog just to check if variables were being passed and they show up in the console after I press the respective variable.

- (IBAction)variablePressed:(UIButton *)sender {
  NSString *variablePressed = [sender currentTitle];
  NSMutableArray *variableValues = [NSMutableArray arrayWithObjects:variablePressed, nil];
  for(int i = 0; i < [variableValues count]; i++) {
    NSLog(@"%@",[variableValues objectAtIndex:i]);
  }
}

Answer 1

To set specific value for specific keys, you could add an NSMutableDictionary to your current class Add it as a property in your class and synthesize it Now when you want to assign a value for "x" you would do the following

//Add this var in your .h file create a property around it
NSMutableDictionary *variables;
//in the .m @synthesize variables;

When assigning the variable "x"

//for example you want to set varialbe "x" = 20
int xValue = 20;
NSString *xVariable = @"x";
[variables setObject:[NSNumber numberWithInt:xValue] forKey:xVariable];

Getting value for "x"

//Later on if you want to get x
NSString *xVariable = @"x";
int xValue = [[variables valueForKey:xVariable] intValue];