Skip to content

FORTRAN if statements

Home arrow Computational arrow FORTRAN arrow FORTRAN if statements


FORTRAN if statements E-mail
User Rating: / 0
PoorBest 
An important part of any programming language are the conditional statements. The most common such statement in Fortran is the ifstatement, which actually has several forms.
The simplest one is the logical ifstatement:
if ( logical expression) executable statement
This has to be written on one line. This example finds the absolute value of x:
if (x .LT. 0) x = -x
If more than one statement should be executed inside the if, then the following syntax should be used:
if ( logical expression) then
statements
endif

The most general form of the if statement has the following form:
if ( logical expression) then
statements
elseif ( logical expression) then
statements
:
:
else
statements
endif

The execution flow is from top to bottom. The conditional expressions are evaluated in sequence until one
is found to be true. Then the associated code is executed and the control jumps to the next statement after
the endif.

Nested if statements
if statements can be nested in several levels. To ensure readability, it is important to use proper indentation.
Here is an example:
if (x .GT. 0) then
if (x .GE. y) then
write(*,*) 'x is positive and x = y'
else
write(*,*) 'x is positive but x < y'
endif
elseif (x .LT. 0) then
write(*,*) 'x is negative'
else
write(*,*) 'x is zero'
endif

You should avoid nesting many levels of if statements since things get hard to follow.
 
[ Back ]