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Home » Tip Bank » C++
Language: C++
Expertise: Beginner
Mar 27, 2000



Building the Right Environment to Support AI, Machine Learning and Deep Learning

Avoid Assignments Inside an If Condition

An assignment expression can appear inside an if condition:

  if (x = getval() )
    // do someting

The if condition is evaluated in two steps: first, the unconditional assignment to x takes place. Then, x is checked. The if block is executed only if x's value (after the assignment) isn't zero. Although this technique can save you a few keystrokes, it's highly dangerous and should be avoided. The problem is that one can easily mistake == for = or vice versa. For this reason, several compilers issue a warning message if you place an assignment expression inside an if condition, to draw your attention to a potential bug. If you need to assign a value and test the result, separate these two steps into two distinct statements as follows:

  x = getval();
  if (x)
    // do someting

This way, you document your intention more clearly and avoid this potential bug.

Danny Kalev
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