External Function Example

• A function is invoked by its appearance in an expression at the place where its result value is needed,

      total = total + largest(a,b,c)

• external functions should be declared as EXTERNAL or else the INTERFACE should be given,

      INTEGER, EXTERNAL :: largest

• The function is defined as follows,

      INTEGER FUNCTION largest(i,j,k)
       IMPLICIT NONE
       INTEGER :: i, j, k
       largest = i
       IF (j .GT. largest) largest = j
       IF (k .GT. largest) largest = k
      END FUNCTION largest

  or equivalently as,

      FUNCTION largest(i,j,k)
       IMPLICIT NONE
       INTEGER :: i, j, k
       INTEGER :: largest
        ...
      END FUNCTION largest

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