creating default vars (objects) in objective c

Question

dumb question: lets say I'm assigning a var in a conditional statement. I don't know if the condition will be satisfied and i still want the var to be defined.. whats the correct way of writing this

example:

    NSDecimalNumber *number = [[NSDecimalNumber alloc]init];  // this is pointless right?

    if(x == z){
        number = [whatevernum1 decimalNumberByMultiplyingBy: whatevernum2];
    } else {
        number = [whatevernum2 decimalNumberByDividingBy: whatevernum3];
    }

    // do something with number variable.

Since number isn't really given a starting value, what's the point of trying to multiply or divide it by whatevernumber? — rmaddy
– rmaddy, Commented Jul 23, 2013 at 21:36

rmaddy · Accepted Answer · 2013-07-23 21:42:37Z

2

There is no need to initialize number since it will be set. Just do this:

NSDecimalNumber *number;

if(x == z){
    number = [whatevernum1 decimalNumberByMultiplying: whatevernum2];
} else {
    number = [whatevernum2 decimalNumberByDividing: whatevernum3];
}

// do something with number variable.

In your case number will be assigned a value one way or another. But you might have a situation like this:

if (someCondition) {
    // set number to value A
} else if (anotherCondition) {
    // set number to value B
}

Here, it is possible that neither condition is met. In this case you need to deal with this properly by initializing number to nil.

NSDecimalNumber *number = nil;

if (someCondition) {
    // set number to value A
} else if (anotherCondition) {
    // set number to value B
}

if (number) {
    // process result
}

answered Jul 23, 2013 at 21:42

rmaddy

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Comments

Benjamin Mayo · Accepted Answer · 2013-07-23 21:40:02Z

0

You need to declare the variable but not assign it, like this:

NSDecimalNumber *number;

if(x == z){
    number = [whatevernum1 decimalNumberByMultiplying: whatevernum2];
} else {
    number = [whatevernum2 decimalNumberByDividing: whatevernum3];
}

This tells the compiler that you want to use a variable named number, but don't have a value for it yet. In some cases, you may find it convenient to initialise the variable to nil rather than leaving it as a null pointer.

answered Jul 23, 2013 at 21:40

Benjamin Mayo

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sapi · Accepted Answer · 2013-07-23 23:53:57Z

0

Normally, as others have pointed out, you would either not initialise (if you can guarantee that you will set a value, eg through an if/else pair), or you would initialise to nil.

In this simple case, a ternary statement would make your code much clearer:

NSDecimalNumber *number = x == z ? [whatevernum1 decimalNumberByMultiplyingBy:whatevernum2] : [whatevernum2 decimalNumberByDividingBy:whatevernum3];

answered Jul 23, 2013 at 23:53

sapi

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