How can I add decimals to my calculator? Percentages as well?

Question

I am building a simple calculator app. I have implemented my calculator this way: I have the viewcontroller.h and .m, I also have my "CalculatorBrain.h and .m" That is where I implement the addition and substraction, multiplication. I use the symbol or the text of the button to read it and calculate the value. The question is, if I have 1.5 plus 1.5, it says the answer is 2. It only takes the 1 and the 1. How do I add decimals? Also, if possible, how would I do percentages?
This is my Calculator Brain.m:
#import "CalculatorBrain.h"
const NSString *Delete = @"D";
@implementation CalculatorBrain
- (void)setOperand:(double)anDouble
    operand = anDouble;
- (void)performWaitingOperation
    if ([@"+" isEqual:waitingOperation]) {
        operand = waitingOperand + operand;
    } else if ([@"-" isEqual:waitingOperation]) {
        operand = waitingOperand - operand;
    } else if ([@"×" isEqual:waitingOperation]) {
        operand = waitingOperand * operand;
    } else if ([@"÷" isEqual:waitingOperation]) {
        if (operand) {
        operand = waitingOperand / operand;
- (double)performOperation:(NSString *)operation;
    if ([operation isEqual:@"√"]) {
        operand = sqrt(operand);
    } else {
        [self performWaitingOperation];
        waitingOperation = operation;
        waitingOperand = operand;
    return operand;
@end
And this is my View Controller.m. Any suggestions?:
#import "CalculatorViewController.h"
@implementation CalculatorViewController
- (CalculatorBrain *)brain
    if (!brain) {
        brain= [[CalculatorBrain alloc] init];
    return brain;
- (IBAction)digitPressed:(UIButton *)sender;
    NSString *digit = [[sender titleLabel] text];
    if (userIsInTheMiddleOfTypingANumber) {
        [display setText:[[display text] stringByAppendingString:digit]];
    } else {
        [display setText:digit];
        userIsInTheMiddleOfTypingANumber = YES;
- (IBAction)operationPressed:(UIButton *)sender;
    if (userIsInTheMiddleOfTypingANumber) {
        [[self brain] setOperand:[[display text] doubleValue]];
        userIsInTheMiddleOfTypingANumber = NO;
    NSString *operation = [[sender titleLabel] text];
    double result = [[self brain] performOperation:operation];
    [display setText:[NSString stringWithFormat:@"%g", result]];
- (void) runTimer;
    // This starts the timer which fires the showActivity
    // method every 0.5 seconds
    myTicker = [NSTimer scheduledTimerWithTimeInterval: 0.5
                                                target: self
                                              selector: @selector(showActivity)
                                              userInfo: nil
                                               repeats: YES];
- (void)showActivity;
    NSDateFormatter *formatter =
    [[NSDateFormatter alloc] init];
    NSDate *date = [NSDate date];
    // This will produce a time that looks like "12:15:00 PM".
    [formatter setTimeStyle:NSDateFormatterMediumStyle];
    // This sets the label with the updated time.
    [clockLabel setText:[formatter stringFromDate:date]]; 
// Implement viewDidLoad to do additional
// setup after loading the view, typically from a nib.
- (void)viewDidLoad {
    [super viewDidLoad];
    // This calls the runTimer method after loading
    // SimpleClockViewController.xib
    [self runTimer];
//  CalcController.m
//  SimpleCalc
//  Created by Chris Ball ([email protected]) on 1/17/08.
//  Copyright 2008, Chris Ball, Strainthebrain.Blogspot.Com.
//  All rights reserved.
- (IBAction)resetEverythingPressed:(UIButton *)sender;
    if (userIsInTheMiddleOfTypingANumber) {
        [[self brain] setOperand:[[display text] doubleValue]];
        userIsInTheMiddleOfTypingANumber = NO;
    NSString *operation = [[sender titleLabel] text];
    double result = [[self brain] performOperation:operation];
    [display setText:[NSString stringWithFormat:@"0", result]];
@end
Oh, by the way, it tells the time. And if you want a screenshot, so you can see how it works out...

Answer 1

For percentages, first make sure the number is < 0, then multiply it by 100, add a % sign and you're done
        double displayValue = [display.text doubleValue];
        if(displayValue < 0)
            displayValue *= 100;
            [display setText:[@"%" stringByAppendingFormat:@"%g", displayValue]];