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POWhy is this NSNumber sum throwing back an odd result?
 

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  1. POWhy is this NSNumber sum throwing back an odd result?
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    <p>I am making an app that deals with calculating money and have read that its always best to use NSNumber for this. So I have changed my float values to NSNumber but now I get the following odd result and I don't know why it is occurring.</p> <p>This is the code:</p> <pre><code>- (NSDecimalNumber*) subtotal { NSDecimalNumber *subtotal = [NSDecimalNumber decimalNumberWithString:@"0"]; NSLog(@"subtotal initially set at %@",subtotal); for (NSManagedObject *object in [fetchedResultsController fetchedObjects]) { NSLog( @"Looping"); NSDecimalNumber *objectRowTotalNumber = [object valueForKey:@"total"]; NSLog(@"object row total number = %@",objectRowTotalNumber); subtotal = [subtotal decimalNumberByAdding:objectRowTotalNumber]; NSLog(@"Subtotal: %@", subtotal); } return 0; } </code></pre> <p>This is the output in the log:</p> <pre><code>**2011-10-19 09:27:19.289 Market[4240:b603] subtotal initially set at 0** **2011-10-19 09:27:19.290 Market[4240:b603] Looping** **2011-10-19 09:27:19.291 Market[4240:b603] object row total number = 5** **2011-10-19 09:27:19.292 Market[4240:b603] Subtotal: -0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000244200806570181766106054656** </code></pre> <p>Would anyone know what is causing the odd result when the subtotal should simple be set to 5?</p> <p><strong>Latest Test</strong> : The NSDecimalNumberMethod works only on new objects that I add in the session, but not on objects that are loaded</p> <pre><code>-(void) viewDidAppear:(BOOL)animated { NSLog(@"I'm in ViewDidAppear"); // Reload subtotal via float method [self subtotal]; //Reload subtotal via decimal method [self subtotalDec]; } </code></pre> <p>Calculating with float method</p> <pre><code>-(float) subtotal { NSLog(@"I'm in subtotal using floats"); float subtotal = 0; NSLog(@"subtotal initially set at %@",subtotal); for (NSManagedObject *object in [fetchedResultsController fetchedObjects]) { NSLog( @"Looping"); NSNumber *objectRowTotalNumber = [object valueForKey:@"total"]; NSLog(@"object row total number = %@",objectRowTotalNumber); float objectRowTotal = [objectRowTotalNumber floatValue]; subtotal = subtotal + objectRowTotal; } NSLog(@"Subtotal: %f", subtotal); return 0; } </code></pre> <p>Calculating with NSDecimal Number Method</p> <pre><code>- (NSDecimalNumber*) subtotalDec { NSLog(@"I'm in subtotal using NSDecimalNumber"); NSDecimalNumber *subtotal = [NSDecimalNumber decimalNumberWithString:@"0"]; NSLog(@"subtotal initially set at %@",subtotal); for (NSManagedObject *object in [fetchedResultsController fetchedObjects]) { NSLog( @"Looping"); NSDecimalNumber *objectRowTotalNumber = [object valueForKey:@"total"]; NSLog(@"object row total number = %@",objectRowTotalNumber); subtotal = [subtotal decimalNumberByAdding:objectRowTotalNumber]; } NSLog(@"Subtotal: %@",subtotal); return 0; } </code></pre> <p>log for view Will appear</p> <pre><code>2011-10-19 11:19:01.506 Market[961:b603] I'm in ViewDidAppear 2011-10-19 11:19:01.506 Market[961:b603] I'm in subtotal using floats 2011-10-19 11:19:01.507 Market[961:b603] subtotal initially set at (null) 2011-10-19 11:19:01.508 Market[961:b603] Looping 2011-10-19 11:19:01.508 Market[961:b603] object row total number = 4 2011-10-19 11:19:01.509 Market[961:b603] Looping 2011-10-19 11:19:01.509 Market[961:b603] object row total number = 1 2011-10-19 11:19:01.509 Market[961:b603] Looping 2011-10-19 11:19:01.510 Market[961:b603] object row total number = 10 2011-10-19 11:19:01.510 Market[961:b603] Subtotal: 15.000000 2011-10-19 11:19:01.510 Market[961:b603] I'm in subtotal using NSDecimalNumber 2011-10-19 11:19:01.511 Market[961:b603] subtotal initially set at 0 2011-10-19 11:19:01.511 Market[961:b603] Looping 2011-10-19 11:19:01.511 Market[961:b603] object row total number = 4 2011-10-19 11:19:01.512 Market[961:b603] Subtotal: -0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000244200806569055866199212032 2011-10-19 11:19:01.512 Market[961:b603] Looping 2011-10-19 11:19:01.512 Market[961:b603] object row total number = 1 2011-10-19 11:19:01.513 Market[961:b603] Subtotal: -0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000488401613129104533143683072 2011-10-19 11:19:01.513 Market[961:b603] Looping 2011-10-19 11:19:01.513 Market[961:b603] object row total number = 10 2011-10-19 11:19:01.514 Market[961:b603] Subtotal: -0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000732602419703789898877108224 </code></pre> <p>log for addbuttontapped: Notice how the NSDecimalNumberMethod works only on the last added value, not on the ones that were entered before the program was started</p> <pre><code>2011-10-20 07:17:03.218 Market[2199:b603] I'm in subtotal using floats 2011-10-20 07:17:03.218 Market[2199:b603] subtotal initially set at (null) 2011-10-20 07:17:03.219 Market[2199:b603] Looping 2011-10-20 07:17:03.219 Market[2199:b603] object row total number = 4 2011-10-20 07:17:03.219 Market[2199:b603] Looping 2011-10-20 07:17:03.219 Market[2199:b603] object row total number = 1 2011-10-20 07:17:03.220 Market[2199:b603] Looping 2011-10-20 07:17:03.220 Market[2199:b603] object row total number = 10 2011-10-20 07:17:03.220 Market[2199:b603] Looping 2011-10-20 07:17:03.221 Market[2199:b603] object row total number = 2 2011-10-20 07:17:03.221 Market[2199:b603] Subtotal: 17.000000 2011-10-20 07:17:03.221 Market[2199:b603] I'm in subtotal using NSDecimalNumber 2011-10-20 07:17:03.222 Market[2199:b603] subtotal initially set at 0 2011-10-20 07:17:03.222 Market[2199:b603] Looping 2011-10-20 07:17:03.222 Market[2199:b603] object row total number = 4 2011-10-20 07:17:03.223 Market[2199:b603] Subtotal: -0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000244200806569055866199212032 2011-10-20 07:17:03.223 Market[2199:b603] Looping 2011-10-20 07:17:03.224 Market[2199:b603] object row total number = 1 2011-10-20 07:17:03.224 Market[2199:b603] Subtotal: -0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000488401613129104533143683072 2011-10-20 07:17:03.224 Market[2199:b603] Looping 2011-10-20 07:17:03.225 Market[2199:b603] object row total number = 10 2011-10-20 07:17:03.225 Market[2199:b603] Subtotal: -0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000732602419703789898877108224 2011-10-20 07:17:03.225 Market[2199:b603] Looping 2011-10-20 07:17:03.226 Market[2199:b603] object row total number = 2 2011-10-20 07:17:03.226 Market[2199:b603] Subtotal: 2 </code></pre>
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    1. COPossible duplicate: http://stackoverflow.com/questions/3897042/adding-nsdecimalnumbers-not-quite-working
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      1. POWhy is this NSNumber sum throwing back an odd result?
      1. USWolfert
    2. COHave you checked if `[object valueForKey:@"total"]` is giving you back an `NSDecimalNumber`?
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      1. POWhy is this NSNumber sum throwing back an odd result?
      1. USOrangenhain
    3. COYes that's the solution! although the total was specified as an NSDecimalNumber according to my object model. I had accidentally fed it an NSNumber. Thanks!! @Orangenhain
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