Fortran/Fortran simple input and output
Default output[edit | edit source]
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 hello_world 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.
File output[edit | edit source]
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 hello_world 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.