arithmetic-if (OB081)

Fix is sometimes available.

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This rule is turned on by default.

What it does

Checks for arithmetic if statements.

Why is this bad?

The arithmetic if statement is used to jump between one of three statement labels depending on whether the condition is below, above, or equal to zero. However, this is incompatible with the IEEE 754 standard on floating point numbers (due to the comparison between reals), and the use of statment labels can hinder optimisation, as well as making the code harder to read and maintain.

Example

    IF(x(1)) 10, 20, 30
10  PRINT *, 'first case'
    GOTO 40
20  PRINT *, 'second case'
    GOTO 40
30  PRINT *, 'third case'
40  CONTINUE

Use instead:

if (x(1) < 0) then
  print*, "first case"
else if (x(1) > 0) then
  print*, "third case"
else
  print*, "second case"
end if