When I started to learn Objective C, that is hard to understand the NSDecimalNumber. I am C# and Java Programmer, in these languages, we used the primitive, such as integer and long, I can just use - and + as operand. However, in IOS, the most of situations, we are using NSDecimalNumber. That is an object. So, you cannot use + and -. If you write this, it will cause error:

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You should use such operands:
decimalNumberByAdding = +
decimalNumberBySubtracting = -
decimalNumberByMultiplyingBy = *
decimalNumberByDividingBy = /
For Example:

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