Adding a decimal point button to an iOS Calculator - objective-c

Question

I followed a tutorial to make an iOS Calculator, and I am now wanting to add a decimal place button to it. Here is my code
header file:
#import <UIKit/UIKit.h>
#interface CalcViewController : UIViewController {
float result;
float selectedNumber;
int selectedOperation;
IBOutlet UILabel *calcScreen;
}
-(IBAction)numberPressed:(id)sender;
-(IBAction)operationPressed:(id)sender;
-(IBAction)clearNumber:(id)sender;
-(IBAction)clearOperation:(id)sender;
#end
Here is my implementation file
#import "CalcViewController.h"
#implementation CalcViewController
-(IBAction)numberPressed:(id)sender {
selectedNumber = selectedNumber * 10 + (float) [sender tag];
calcScreen.text = [NSString stringWithFormat:#"%2g", selectedNumber];
}
-(IBAction)operationPressed:(id)sender {
if (selectedOperation == 0) {
result = selectedNumber;
} else {
switch (selectedOperation) {
case 1:
result = result + selectedNumber;
break;
case 2:
result = result - selectedNumber;
break;
case 3:
result = result * selectedNumber;
break;
case 4:
result = result / selectedNumber;
break;
case 5:
selectedOperation = 0;
break;
}
}
selectedNumber = 0;
calcScreen.text = [NSString stringWithFormat:#"%2g", result];
if ([sender tag] == 0) result = 0;
selectedOperation = [sender tag];
}
-(IBAction)clearNumber:(id)sender {
selectedNumber = 0;
calcScreen.text = #"0";
}
-(IBAction)clearOperation:(id)sender {
selectedNumber = 0;
calcScreen.text = #"0";
selectedOperation = 0;
}
I saw on another thread that someone had suggesting using the method:
- (IBAction)Decimal:(id)sender
{
NSString *currentText = calcScreen.text;
if ([currentText rangeOfString:#"." options:NSBackwardsSearch].length == 0) {
calcScreen.text = [calcScreen.text stringByAppendingString:#"."];
}
However this did not seem to work for me. It would indeed let me enter a decimal point, but when a second number was entered the decimal point would be lost. Can anyone suggest a method I could implement to achieve what I am trying to?
Cheers in advance!

Answer 1

My quick thought: keep the number as text on the screen, adding additional digits and/or decimal point to it as text. Only convert it to a float (I would use double myself, btw) at the moment that an operation is performed. The suggested method should then work fine.
Something like:
-(IBAction)numberPressed:(id)sender {
calcScreen.text = [calcScreen.text stringByAppendingString:[sender tag]];
}
-(IBAction)operationPressed:(id)sender {
selectedNumber = [calcScreen.text floatValue];
...
}

Answer 2

One quick tip, instead of using
int selectedOperation;... and later in code
switch (selectedOperation) {
case 1:
result = result + selectedNumber;
break;
case 2:
result = result - selectedNumber;
...
Try using typedef enum
typedef enum {
OperationTypeAdd = 0,
OperationTypeSub,
...
} OperationType
and in switch block
switch (operationType) {
case OperationTypeAdd:
result = result + selectedNumber;
break;
case operationTypeSub:
result = result - selectedNumber;
break;