Why is the Order of Evaluation of Operands Unspecified in C ?

Order of Evaluation of Operands in C

In mathematical expressions, the order of evaluation of operands is often assumed to be fixed. However, in programming languages like C , the order of evaluation can be unspecified, leading to unexpected results.

Consider the expression a b. In this expression, the operands a and b can be evaluated in any order. This is known as "unspecified order of evaluation."

The C standard specifies that the order of evaluation of function arguments and operands of individual operators is unspecified. This means that the compiler is free to evaluate the operands in any order it chooses.

For example, consider the following code:

<code class="cpp">int main() {
  int a = 1;
  int b = 2;
  int c = a + b;
  printf("%d", c);
  return 0;
}</code>

In this code, the order of evaluation of a and b is unspecified. The compiler could evaluate a first, or b first. The result of the expression a b could be either 3 or 4, depending on the order of evaluation.

Uncertain evaluation order can lead to bugs in your code. To ensure predictable behavior, it is important to understand the order of evaluation for the specific operators and expressions you are using.

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