Fortran/Fortran simple input and output
C. PROGRAM TO EVALUATE SUM OF FINITE SERIES
WRITE(*,*)`ENTER THE VALUE OF X' READ(*,*)X WRITE(*,*)'ENTER THE VALUE OF N' READ(*,*)N SUM=0.0 DO 10I=1,N TERM=((-1)**I)*(X**(I*0.5))/I*(I+1)) SUM=SUM+TERM
10 CONTINUE WRITE (*,*)`SUM OF SERIES'=,SUM PAUSE STOP END
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:
Hello World!
If one had put "Hello World!" in one print statement, the text "Hello World!" would have appeared on one line.