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Side effects
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According to Wikipedia, a function or expression is said to have a side effect if it modifies some state outside its local environment.
In this figure, we have a variable x that is outside the scope of two functions. Clearly, after the Function_2 call, the value of x changes which means that Function_2, other than returning value(if any), is interacting with variables outside its local environment and thus has a side effect.
In general, any lasting effect that occurs in a function, not through its return value, is called a side effect.
