How Much Does Operator Precedence Really Define Evaluation Order in Programming?

Redundancy of Operator Precedence and Evaluation Order

In programming, operators are evaluated in a specific order to determine the result of an expression. This order is governed by the concept of operator precedence. However, it should be noted that operator precedence and order of evaluation are not synonymous.

For example, consider the expression x < y < z. Based on operator precedence, this expression would typically be parsed as (x < y) < z. However, the order of evaluation is not explicitly defined by operator precedence. It is possible for the evaluation to occur in the sequence: z, x, y, resulting in a different outcome.

This distinction becomes apparent when considering side effects associated with expressions. For instance, the expression a = b c involves the use of pre- and post-increment operators. While the order of evaluation could be such that a becomes b before c is incremented, the increment operations are ultimately guaranteed to occur before the sequence point at the end of the statement.

In essence, order of evaluation determines when operators are applied, but undefined behavior may result if the value of a variable is used before a subsequent side-effect-producing operation has occurred. The order of evaluation is not consistently defined in the C language standard, and implementations may vary in how they approach specific situations.

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