CSCE150 Fortran Lab 4

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CSCE150 Fortran Lab 4
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outline

• Branching Structures
• if then else
• select case
• Exercise 1
• Exercise 2
• Exercise 3

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Branching Structures

• if then else
• (section 3.4.1 and 3.4.2 page 96)
• Used for binary condition judgment (True/False)
• Example1
• INTEGER a
• IF (agt0) THEN
• WRITE (,) a is positive
• END IF

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• the IF () THEN is a single Fortran statement
• they must be written together on the same line
• the statements to be executed must occupy
  separate lines following the IF () THEN
  statement
• an END IF statement must follow them on a
  separate line

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• Example2
• INTEGER a
• IF (agt0) THEN
• WRITE (,) a is positive
• ELSE
• WRITE (,) a is not positive
• END IF
• an ELSE statement must occupy a line by itself

• Example3
• INTEGER a
• IF (agt0) THEN
• WRITE (,) a is positive
• ELSE IF (alt0) THEN
• WRITE (,) a is negative
• ELSE
• WRITE (,) a is zero
• END IF

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Branching Structures

• select case
• (section 3.4.7 page 111)
• Used for multiple selection judgment (multiple
  choices and treatments)

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• Example
• INTEGERa
• SELECT CASE (a)
• CASE (0)
• WRITE(,) a is zero
• CASE (1)
• WRITE(,) a is positive
• CASE (-1)
• WRITE(,) a is negative
• CASE DEFAULT
• WRITE(,) impossible entry
• END SELECT

• Example 3 of Ifthenelse
• INTEGER a
• IF (agt0) THEN
• WRITE (,) a is positive
• ELSE IF (alt0) THEN
• WRITE (,) a is negative
• ELSE
• WRITE (,) a is zero
• END IF

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• review and compare the example 3 of if then
  else and the example of select case
• select case branching structure can always be
  implemented by if then else structure

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Exercise 1

• Write a Fortran program to convert a score to a
  grade (use ifthenelse)
• 90-100 A
• 80-89 B
• 70-79 C
• 60-69 D
• 0 - 59 F
• the score (less than 100) is specified by the
  user
• print the corresponding grade to the screen

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Exercise 2

• triangle judgment
• Recall from high school geometry that the sum of
  any two sides of a triangle must be strictly
  greater than the third.
• That is, for sides a, b and c, the inequalities
• abgtc
• acgtb
• bcgta
• must all hold.

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• Write a Fortran program to
• get three values from the user
• check whether the inputs could form a valid
  triangle or not
• if the inputs can form a triangle, print a
  message Valid triangle! to the screen
• otherwise, print Invalid triangle!

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• relational operators
• Section 3.3.3 on page 91
• combinational logic operators
• Section 3.3.4 on page 92
• Show me
• your code
• result of the test case
• 6, 8, 10 gt Valid triangle!
• 5, 6, 1 gt Invalid triangle!

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Exercise 3

• write a Fortran program to convert a score to a
  grade (use select case)
• 90-100 A
• 80-89 B
• 70-79 C
• 60-69 D
• 0 - 59 F
• the score (less than 100) is specified by the
  user
• print the corresponding grade to the screen