1. LAB-06 IF + Functions I Putu Danu Raharja raharja @kfupm.edu.sa
Information & Computer Science Department
CCSE - King Fahd University of Petroleum & Minerals

2. Rationale
If you work on a program to solve a bigger problem, your program will become larger (more lines of code).
A large program is harder to debug (so far we have written programs < 100 lines but we still make mistakes)
Some of the code may be used several times.
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3. Subprogram
A big problem can be solved by dividing it into smaller sub-problems and conquering the sub-problems
A large program can be divided into simpler sub-programs that can be implemented and tested independently
Sub-programs can be reused
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4. Terminologies Main program Sub-program Call & return Function
Subroutine
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5. Function A function consists of:
Function header
Function body
type FUNCTION fname (list of arguments)
Declaration statements
Executable statements
Must have at least one RETURN statement
Must be ended with an END statement
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6. Example: Area of a triangle
REAL FUNCTION TRAREA (A, B)
REAL A, B
TRAREA = A * B / 2
RETURN
END
REAL X, Y, AREA
READ*, X, Y
AREA = TRAREA(X, Y)
PRINT*, 'Area = ', AREA
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7. Intrinsic Functions
Functions which are available from the FORTRAN language (p. 63)
SQRT(X)
ABS(X)
SIN(X)
COS(X)
TAN(X)
EXP(X)
LOG(X)
LOG10(X)
INT(X)
REAL(K)
MOD(M, N)
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8. Statement Function Expressed as:
fname (list of arguments) = expression
Example:
TRA (BASE, HEIGHT) = BASE * HEIGHT * 0.5
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9. Exercises
A year with 366 days is called a leap year. A year is a leap year if it is divisible by 4 (for example, 1980), except that it is not a leap year if it is divisible by 100 (for example, 1900); however, it is a leap year if it is divisible by 400 (for example, 2000). There were no exceptions before the introduction of the Gregorian calendar on October 15, 1582 (for example, 1500 was a leap year). Write a logical function to determine whether the given year is a leap year.
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10. Exercise
Write a function that takes month and year as arguments and returns the number of days of that month.
Write a function that takes two real numbers and tests whether they are the same up to two decimal places.
Write a function that takes two times (hour and minute) in military format (09:00, 17:30) and computes the number of hours between the two times. You have to consider the case that the first time is later than the second time.
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