There are a variety of control constructs available in Fortran. The most essential ones are the if-then-else construct and the loop construct (do). An if-then-else construct looks like this:

If the logical expression evaluates to .true., then the associated code block is executed. If not, the next else if statement is evaluated, or the else branch is executed. The else if and the else parts of the construct are optional.

The logical expression may use these symbols: