# Interview Questions

# Order of evaluation of operands

What will be the output of the below code in C or C++ language?

int x = 0; int a() { x = 10; return 2; } int b() { x = 20; return 3; } main() { int y = a() + b(); printf("%d", x); }

The value of y will definitively be 5. Because function a() returns a constant value 2, and function b() returns a constant value 3.

But that’s not the question because what is getting printed is the value of x.

x is a global variable initialized to zero. Function a() sets the value of x to 10 and Function b() sets the value to 20.

In expression

y = a() + b();

The order in which function a() and b() will be called (which function gets called first) depends on the Order Of Evaluation of Operands for plus operator.

*If plus operator evaluates its operand from Left to Right like below:*

First a() will be called (which will set the value of x to 10) Then, function b() will be called which will set the value of x to 20. Hence, the final value of x will be 20.

**If plus operator evaluates its operands from Right To Left as below:**

First b() will be called (which will set the value of x to 20) Then, function a() will be called which will set the value of x to 10. Hence, the final value of x will be 10.

So, the final value of x depends on the order in which operands of plus operator are getting evaluated.

The Standard says, “*Order of Evaluation of operands for plus operator is not defined*“. This order has to be defined by the Compiler.

Hence the answer to the original question is *“Not Defined”* or *“Compiler Dependent”*.