9.2: EXIT and CYCLE Statements

Last updated
Save as PDF

Page ID: 54280

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

The exit and cycle statements are used to modify the execution of a do-loop. The exit statement is used to exit a loop. The exit can be used alone, but it is typically used with a conditional statement to allow exiting a loop based on a specific condition. The exit statement can be used in a counter controlled loop or a conditionally controlled loop.

For example, given the following declarations,

integer :: i

the following loop,

do i = 1, 10
    if (i == 5) exit
    write (*,*) i
end do

will display the numbers from 1 to 4 skipping the remaining iterations. Since the variable \(i\) is checked before the write statement, the value is not displayed with \(i\) is 5 and the loop is exited without completing the remaining iterations. While it is possible to have multiple exit statements, typically only one is used. However, multiple exit statements may be required for more complex problems.

The cycle statement will skip the remaining portion of the do-loop and start back at the top. The cycle statement can be used in a counter controlled loop or a conditionally controlled loop. If the cycle statement is used within a counter controlled loop, the next index counter is updated to the next iteration, which could terminate the loop.

For example, given the following declarations,

integer :: i

the following loop,

do i = 1, 10
    if (i == 5) cycle
    write (*,*) i
end do

will display the numbers from 1 to 4 and 6 to 10.