Listed-Directed Output: The WRITE Statement

Listed-directed output is carried with the Fortran WRITE statement. The WRITE statement can display the results of a set of expressions and character strings. In general, WRITE displays the output on the screen.

The WRITE statement has the following forms:

WRITE(*,*)  exp1, exp2, ..., expn
WRITE(*,*)

The first form starts with WRITE(*,*), followed by a list of arithmetic expressions or character strings, separated by commas. The computer will evaluate the arithmetic expressions and displays the results. Note that if a variable does not contain a value, its displayed result is unpredictable. The second form only has WRITE(*,*), which has a special meaning.

The following example displays the values of four variables on screen:

INTEGER  ::  Factor, N
REAL     ::  Multiple, tolerance

WRITE(*,*)  Factor, N, Multiple, tolerance

The following example displays the string content of Title, followed by the result of (Height + Length) * Area.
```
CHARACTER(LEN=10)  :: Title
REAL               :: Height, Length, Area

WRITE(*,*)  Title, (Height + Length) * Area
```

There are some useful rules:

Each WRITE starts with a new line.

Consequently, the second form in which the WRITE does not have a list of expressions just displays a blank line.

INTEGER                     ::  Target
REAL                        ::  Angle, Distance
CHARACTER(LEN=*), PARAMETER ::  Time = "The time to hit target "    &
                                IS   = " is "                       &
                                UNIT = " sec."

Target   = 10
Angle    = 20.0
Distance = 1350.0
WRITE(*,*)  'Angle    = ', Angle
WRITE(*,*)  'Distance = ', Distance
WRITE(*,*)
WRITE(*,*)  Time, Target, IS, Angle * Distance, UNIT

This example may produce the following result:

Angle    = 20.0
Distance = 1350.0

The time to hit target 10 is 27000sec.

The blank line is generated by the third WRITE.

The above example uses assumed length specifier (i.e., LEN=*) and continuation lines (i.e., symbol &).

If there are too many results that cannot be fit into a single line, the computer will display remaining results on the second, the third line and so on.

Output Format:

There is nothing to worry about the output format. The computer will use the best way to display the results. In other words, integers and real numbers will be displayed as integers and real numbers. But, only the content of a string will be displayed. The computer will also guarantee that all significant digits will be shown so that one does not have to worry how many positions should be used for displaying a number. The consequence is that displaying a good-looking table is a challenge. This will be discussed in FORMAT statement.