Fortran/Fortran simple input and output
A Fortran program reads from standard input or from a file using the read statement, and it can write to standard output using the print statement. With the write statement one can write to standard output or to a file. Before writing to a file, the file must be opened and assigned a unit number with which the programmer may reference the file. If one wishes to use the write statement to write a statement to the default output, the syntax is write(*,*). It is used as follows:
program HelloWorld implicit none write(*,*) "Hello World!" end program
This code writes "Hello World!" to the default output (usually standard output, the screen), similar to if one had used the print* statement.
As a demonstration of file output, the following program reads two integers from the keyboard and writes them and their product to an output file:
program xproduct implicit none integer :: i,j integer, parameter :: out_unit=20 print*,"enter two integers" read (*,*) i,j open (unit=out_unit,file="results.txt",action="write",status="replace") write (out_unit,*) "The product of",i," and",j write (out_unit,*) "is",i*j close (out_unit) end program xproduct
The file "results.txt" will contain these lines:
The product of 2 and 3 is 6
Each print or write statement on a new line by default starts printing on a new line. For example:
program HelloWorld implicit none print*,"Hello" print*,"World!" end program
Prints, to standard output:
If one had put "Hello World!" in one print statement, the text "Hello World!" would have appeared on one line.