Accessing elements of an array, Objective-C

Question

I'm trying to access the elements of an array and change them such as I have an array with numbers and variables x, I have to go through the array and replace the variables x with values. I tried this but I get an error at the for statement which is Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 3 beyond bounds [0 .. 2]'

 if( [stack containsObject:@"X"] )
    {
    int x;
    for(x=0; [stack objectAtIndex:x] ;x++)
    {
    [stack replaceObjectAtIndex:x withObject:[variableValues objectForKey:@"X"]];
    }

is tried doing isEqualToString but it gives me an error there too — Terrel Gibson
– Terrel Gibson, Commented Jul 10, 2012 at 6:19
you would need a loop on stack to check the if condition with isEqualTOString: — Saurabh Passolia
– Saurabh Passolia, Commented Jul 10, 2012 at 6:24

D.C. · Accepted Answer · 2012-07-10 06:26:22Z

1

What is the error you are getting? Could be a couple of things looking at your code. if the array is length zero, then accessing object at index 0 will throw an error. Also, the array needs to be mutable for the replacing to work.

-- update Also, if your objectForKey returns nil, in the replacement method, trying to replace nil will also throw an error. See updated code below:

if( [stack containsObject:@"X"] )
{
    assert([stack isKindOfClass:[NSMutableArray class]] );
    NSUInteger count = [stack count];
    for(NSUInteger x = 0; x < count ;x++)
    {
        id value = [variableValues objectForKey:@"X"];
        if ( value != nil )
        {
            [stack replaceObjectAtIndex:x withObject:value];
        }
    }
}

answered Jul 10, 2012 at 6:26

D.C.

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2 Comments

Terrel Gibson Over a year ago

Why would u have to state the value variable in the for loop? why not just state it before the for loop?

Terrel Gibson Over a year ago

I tried the method above but the problem is that it would replace all objects in the NSMutableArray, so I tried adding if(value != nil && [value isEqualToString:@"X"]) but i get the error [__NSCFNumber isEqualToString:]: unrecognized selector sent to instance. how would I do a comparison to see if the variable in the stack is equal to x?

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