Калькулятор для чисел с десятичной точкой

#import <Cocoa/Cocoa.h>
 
enum
{
    OP_PLUS = 1001,
    OP_MINUS = 1002,
    OP_MULT = 1003,
    OP_DIV = 1004,
    OP_INV = 1005,
    OP_EQUALS = 1006,
};
 
@interface CalcController : NSObject
{
    IBOutlet NSTextField *text;
    BOOL enterFlag;
    BOOL yFlag;
    int  operation;
    double x, y;
}
 
- (IBAction)clear:(id)sender;
- (IBAction)clearAll:(id)sender;
- (IBAction)digit:(id)sender;
- (IBAction)operation:(id)sender;
- (IBAction)invSign:(id)sender;
- (IBAction)decimal:(id)sender;
- (void) displayX;
@end

#import "CalcController.h"
 
@implementation CalcController
- (IBAction)clear:(id)sender
{
    x = 0;
    [self displayX];
}
 
- (IBAction)clearAll:(id)sender
{
    x = 0;
    y = 0;
    yFlag = NO;
    enterFlag = NO;
    [self displayX];
}
 
- (IBAction)digit:(id)sender
{
    if (enterFlag)
    {
        x = x;
        x = 0;
        enterFlag = NO;
    }
    x = (10.0 * x) + [[sender selectedCell] tag];
    [self displayX];
}
 
- (IBAction)operation:(id)sender
{
    if (yFlag)
    {
        switch (operation)
        {
            case OP_PLUS:
                x = y + x;
                break;
            case OP_MINUS:
                x = y - x;
                break;
            case OP_MULT:
                x = y * x;
                break;
            case OP_DIV:
                x = y / x;
                break;
        }
    }
    y = x;
    yFlag = YES;
    operation = [[sender selectedCell] tag];
    enterFlag = YES;
    [self displayX];
}
 
- (IBAction)invSign:(id)sender
{
    x = -x;
    [self displayX];
}
 
- (void) displayX
{
    NSString * str = [NSString stringWithFormat: @"%15.10g", x];
    [text setStringValue: str];
}
@end

-(IBAction)decimal:(id)sender
{
    NSString *str = (NSString* )[sender currentTitle];
    
    if(current != @"")
    {
        if([current isEqualToString: @"."])
        {
            NSRange match;
            match = [current rangeOfString: @"."];
            if(match.location == 0)
            {
                current = [textViewerAmount.text stringByAppendingString:str];
            }
        }
        else
        {
            current = [textViewerAmount.text stringByAppendingString:str]; 
            [textViewerAmount setText:current];
            [self doCalculate];
        }
    }
    else
    {
        current = str;
        [textViewerAmount setText:current];
        [self doCalculate];
        current = @"1";
    }
}