Objective-C blocks and variables

It's because the block captures variables by value and when the block is created (unless you use __block).

What you probably want is:

NSArray *array = @[@25, @"abc", @7.2];

void (^print)(NSUInteger index) = ^(NSUInteger index)
{
    NSLog(@"%@", array[index]);
};

for (int n = 0; n < 3; n++)
    print(n);

Example with __block:

__block NSArray *array;

void (^print)(NSUInteger index) = ^(NSUInteger index)
{
    NSLog(@"%@", array[index]);
};

array = @[@25, @"abc", @7.2];

for (int n = 0; n < 3; n++)
    print(n);

Note that it's a little less efficient to use __block if you don't actually need to modify the variable inside the block and have it reflected outside.

The block captures the array pointer at creation. You can add __block modifier to have the block capture the pointer by reference, but this is usually costly and not recommended. It is better to have the capturing block created after the data is ready to use inside the block.