Looping Control Structure

Most important control structure after branching (If (condition) then-statement)

2 important types of DO-loops in Fortrant

• While Loop construct

                 DO
                     statement 1
                         ...
                     If (condition)  EXIT
                         ...
                     statement n
                 End DO
  

  Loop body is repeatedly executed until (condition) holds and then we exit. How many times is not known in advance!

• Counter based Loop

                 DO I = 1, 100, 1
                     statement 1
                         ...
                         ...
                     statement n
                 End DO
  

  Loop body is executed a fixed number of times (100 above) with counter taking values from 1 to 100 with increments of 1. That is I = 1, I = 2, I = 3, .... , I = 100.