036. Reading user input#

topic: Input and Output

The read statement is used to get data from the terminal or a file. To handle errors, set the iostat in the read call and check afterwards if it is zero.

This program prompts the user for integers, one at a time, and prints their sum.

read-sum.f90 | | 0 | Godbolt Compiler Explorer logo | Fortran logo#
program sum_int
   implicit none
   integer :: i, ierr, isum

   isum = 0
   do
      print *, "enter an integer, 0 to stop"
      read (*, *, iostat=ierr) i
      if (ierr /= 0) then
         print *, "invalid input"
         cycle  ! return to beginning of loop
      end if
      if (i == 0) exit
      isum = isum + i
   end do
   print *, "sum is", isum

end program sum_int
Input#
1
1
2
3
0
Output1#
 enter an integer, 0 to stop
 enter an integer, 0 to stop
 enter an integer, 0 to stop
 enter an integer, 0 to stop
 enter an integer, 0 to stop
 sum is           7
1

Compiled using GNU Fortran (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0 with no flags