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Using Numbers

NSNumber is a subclass of NSValue that offers a value as any C scalar (numeric) type. It defines a set of methods specifically for setting and accessing the value as a signed or unsigned char, short int, int, NSInteger, long int, long long int, float, or double, or as a BOOL. It also defines a compare: method to determine the ordering of two NSNumber objects.

NSInteger nine = 9;

float ten = 10.0;

NSNumber *nineFromInteger = [NSNumber numberWithInteger:nine];

NSNumber *tenFromFloat = [NSNumber numberWithFloat:ten];

NSComparisonResult comparison = [nineFromInteger compare:tenFromFloat];

// comparison = NSOrderedAscending

float aFloat = [nineFromInteger floatValue];

// aFloat = 9.0

BOOL ok = [tenFromFloat boolValue];

// ok = YES

An NSNumber object records the numeric type with which it is created, and uses the C rules for numeric conversion when comparing NSNumber objects of different numeric types and when returning values as C numeric types. See any standard C reference for information on type conversion. (Note, though, that if you ask a number for its objCType, the returned type does not necessarily match the method the receiver was created with.)

If you ask an NSNumber object for its value using a type that cannot hold the value, you get back an erroneous result—for example, if you ask for the float value of a number created with a double that is greater than FLT_MAX, or the integer value of a number created with a float that is greater than the maximum value of NSInteger.

NSNumber *bigNumber = [NSNumber numberWithFloat:(FLT_MAX)];

NSInteger badInteger = [bigNumber integerValue];

NSLog(@"bigNumber: %@; badInteger: %d", bigNumber, badInteger);

// output: "bigNumber: 3.402823e+38; badInteger: 0"

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