If and Else if Statement - objective-c

Question

Im wondering why this code won't work. It's for a calculator :)
I need the symbol (banana) to be recognised by the calculator and to use either +,- according to what the user inputs.
NSString *list = [Sum_TextField text];
NSArray *listItemsArray = [list componentsSeparatedByString:#" "];
int batman = [[listItemsArray objectAtIndex: 0] intValue];
NSString *banana = [listItemsArray objectAtIndex: 1];
int joker = [[listItemsArray objectAtIndex: 2] intValue];
{
Calculator* calc = [[Calculator alloc] init];
[calc setNum1:batman];
[calc setNum2:joker];
if ((banana = #"-"))
{
[calc minus];
}
else if ((banana = #"+"))
{
[calc add];
}
[Answer_TextField setText:[NSString stringWithFormat:#"%d", [calc answer]]];
}
}

Answer 1

To judge whether NSString is equal, you must use [#"AAAA" isEqualToString : #"BBBB"]. You can not use == , because they are not in the same address of the memory .

Answer 2

Here's how you want to do this:
if ([banana isEqualToString:#"-"])
{
[calc minus];
}
else if ([banana isEqualToString:#"+"])
{
[calc add];
}

Answer 3

= is assignment. It has absolutely nothing to do with comparison.
== is comparing the 2 expressions and see whether they are equal. This can be used to compare integral types (such as enum, char, int, short, long, long long, BOOL) or reference (check whether 2 pointers are pointing to the same object). Note that 2 pointers can point to 2 different object which contains the same value inside, but == will compare them as different. (Floating point type such as float and double requires a bit different method to compare equality).
As a method to preempt confusion between = and ==, for equality testing with ==, some people put the value on the left hand side, and the variable on the right hand side (e.g. 2 == variable). If they happen to mistype == to =, the compiler will complain.
If you want to compare the content of 2 objects, in this case is NSString, you should search for isEquals type of function. For NSString, you should use isEqualToString if you want to compare whether the 2 strings have the same content.