how to add int value from array to NSNumber?

Here is my code

I'm looping through the array and adding to the NSNumber.

NSNumber *totalValue = 0; 
NSMutableArra开发者_如何转开发y *items = [10, 35, 25]; // Just for demo
for (int i=0; i < items.count; i++)
{
    totalValue = totalValue + [items objectAtIndex:i] // How do I add the totalValue?
}

Can someone help me with this code?

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NSNumber is an Objective-C class. Unlike in C++, operators cannot be overloaded in Objective-C so you have to call everything manually.

NSNumber *totalValue = [NSNumber numberWithInt:0];
for(…) {
  totalValue = [NSNumber numberWithInt:[totalValue intValue] + [[items objectAtIndex:i] intValue]];
}

You might want to use NSInteger instead, which is faster (especially for a large number of items: memory allocation is expensive):

NSInteger totalValueInteger = 0; // no pointer, NSInteger is a POD!
for (…) {
  totalValueInteger += [[items objectAtIndex:i] integerValue];
}
NSNumber *totalValue = [NSNumber numberWithInteger:totalValueInteger];

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You should really only use NSNumber when you need an Objective-C object, like in an array, dictionary or coder. Otherwise, use a POD like NSInteger, int or double.

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First of all, you can probably do this entire thing using KVC:

NSNumber *total = [items valueForKeyPath:@"@sum.integerValue"];

But to answer your original question, NSNumber is immutable which means you can't change it or increment its value. Creating a new NSNumber on each iteration of your loop is inefficient and wasteful.

You should use a standard int or NSInteger to sum up the total, and then convert the resulting value to an NSNumber at the end if you need it like that.

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Might as well make the intermediate an int.

int temp = 0;
for(…) {
  temp += [[items objectAtIndex:i] intValue];
}
NSNumber *totalValue = [NSNumber numberWithInt:temp];