appending array in objective c

i read this command from cocoadev.com but was not able to get i开发者_运维技巧t plz help me in explaining what this line of code do

[array addObject:[NSNumber numberWithInt:15]];

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You have to use NSMutableArray instead of NSArray to use the method addObject:.

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It adds a number object with the integer value of 15 to the collection (presumably an NSMutableArray) called array.