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FORTRAN 77 Programming.

FORTRAN 77 Programming. Lecture 4 : January 2001 Dr. Andrew Paul Myers. The Story So Far…. FORTRAN 77 program structure. PROGRAM <program name> <comment(s)> <declaration(s)> <assignment(s)> <statement(s)> END. Intrinsic or Extrinsic?. So far we have seen :

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FORTRAN 77 Programming.

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  1. FORTRAN 77 Programming. Lecture 4 : January 2001 Dr. Andrew Paul Myers

  2. The Story So Far… • FORTRAN 77 program structure. PROGRAM <program name> <comment(s)> <declaration(s)> <assignment(s)> <statement(s)> END

  3. Intrinsic or Extrinsic? • So far we have seen : value = SIN( angle_in_radians ) • Every angle has to be converted to radians with the same formula. Very repetitive!

  4. This Would Be Nice… • FORTRAN 77 does not have a degrees to radians function, but one would be useful. e.g. radians = RAD(degrees) or value = SIN ( RAD ( degrees ) )

  5. We Can Do It! • FORTRAN allows you to define your own functions! • They conform to all the rules of intrinsic functions. • Must return a single value. • Defined after the END statement of the main program.

  6. A Simple Function. REAL FUNCTION radians(degrees) REAL degrees,pi,temp pi=4.0*ATAN(1.0) temp=(pi*degrees)/180.0 radians=temp RETURN END

  7. More Complex. REAL FUNCTION power(x,y) REAL temp,x INTEGER loop,y temp=1 DO loop=1,y temp=temp*x END DO power=temp RETURN END

  8. Subroutines. • Another method for “structuring” your program. • Subroutines do not return a value. • Subroutines may change none, one or many of the parameters passed to them.

  9. Definition. SUBROUTINE print_at(message,line) CHARACTER message*80 INTEGER loop,line DO loop=1,line-1 print* END DO PRINT*,message RETURN END

  10. Calling Subroutines. • The CALL statement is used to call subroutines. • Parameter data types must match in the main program and subroutine. CALL print_at(‘Hello!’,10)

  11. Memory Allocation! • The compiler reserves memory for arrays. Consider… CALL bad(100) SUBROUTINE bad(n) INTEGER n REAL array(n)

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