Recursive Function Example

The following example calculates the factorial of a number and uses n! = n(n-1)!

    PROGRAM Mayne
     IMPLICIT NONE
      PRINT*, fact(12) ! etc
    CONTAINS
     RECURSIVE FUNCTION fact(N) RESULT(N_Fact)
      INTEGER, INTENT(IN)  :: N
      INTEGER :: N_Fact ! also defines type of fact
       IF (N > 0) THEN
         N_Fact = N * fact(N-1)
       ELSE
         N_Fact = 1
       END IF
     END function FACT
    END PROGRAM Mayne

To calculate 4!,

1. 4! is , so calculate 3! then multiply by 4,
2. 3! is , need to calculate 2!,
3. 2! is , 1! is and 0! = 1
4. can now work back up the calculation and fill in the missing values.

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