FORTRAN

UNIT 4 
SELECTION STATEMENT

Selection statement or selection construct or selection structures is also called conditional or decision statement. The purpose is to make your program select a result from an option or from a list of options, when a specified condition is met.

4.1       PROGRAMS LAB EXAMPLES

4.1.1   Simple If Statement

In simple if statement, only a single condition is evaluated, the if-block is executed, if the condition is true.

Syntax:

if condtion then     !statements end if

 

4.1.2   Lab 1 – program to test the age of a student, if he eligible to vote

program lab1   !declare variable integer :: age   !display user action and accept information print *, 'Enter your age' read*, age   !test and display !test if age <18, show 'teenager…’ if (age <18) then     print*, 'You are a teenager, you cannot vote' end if end program lab1

 

4.1.3   If…else Statement

In if…else statement, when the condition of the if-block is evaluated to false, the statements in the else block, will get executed.

Syntax:

if condtion then     !statements else     !statements end if

 

4.1.4   Lab 2 – program to test the age of a student, if he eligible to vote

program lab2   !declare variable integer :: age   !user action and accept information print *, 'Enter your age' read*, age   !test and display !test if age <18, show 'teenager…’ if (age <18) then     print*, 'You are a teenager, you cannot vote' else     print*, 'You are an adult, you can vote' end if end program lab2

 

4.1.5   If…else…if…else Statement

In if…else…if….else statement, multiple conditions are evaluated, it is only the block that satisfies the specified condition that will get executed. You can add as many else-if-blocks as you want.

Syntax:

if condition_1 then    ! statements   else if condition_2 then          ! statements   else if condition_3 then          ! statements else          ! statements end if

 

4.1.6   Lab 3 – program to test the classification of patient’s BMI (Body Mass Index), using the table below.

BMI	CLASSIFICATION
< 18.5	Under weight
18.5 to < 25	Normal
25 to < 30	Over weight
> =30	Obesity

!code

program lab3   !declare variable   real :: weight, height, resultBmi    !user action (what user should do) and accept input print *, 'Enter weight value in KG' read*, weight   print *, 'Enter height value in meters from (0-2)' read*, height    !processing resultBmi = weight / (height * height)    !display output print *,'The BMI is:: ' print '(f6.2)', resultBmi     if (resultBmi .lt. 18.5) then     print *,'Your BMI is Under weight' else if ((resultBmi .gt. 18.5) .and. (resultBmi .lt. 25))  then     print *,'Your BMI is Normal'   else if ((resultBmi .gt. 25) .and. (resultBmi .lt. 30))  then     print *,'Your BMI is Over weight'   else if (resultBmi .gt. 30) then     print *,'Your BMI is Obesity'   else     print *,'Something went wrong' end if end program lab3

TIP: Take note of how we wrap the expressions for the condition inside parentheses. Then, fortran logical and is ‘.and.’ (period and keyword and period), also, Fortran relational operator for greater than is ‘.gt.’ while for less than is ‘.lt.’. That is to say, you have to use the correct two-letter abbreviation enclosed by dots!

4.1.7   Lab 4 – program for a user to select his/her gender (take/read/accept character input from the user), using the table below.

Value	CLASSIFICATION
M	Male
F	Female
When the user enters something else	Something went wrong

TIP: We will use the equality operator ‘.EQ.’ and the OR operator ‘.OR.’.

Fortran

program lab4  !declare variable  character :: gender  !user action (what user should do) and accept input print *, 'Enter m/f to select your gender' read*, gender   !test and display output  if ((gender .eq. 'm') .or. (gender .eq. 'M')) then     print *,'Male'   else if ((gender .eq. 'f')  .or. (gender .eq. 'F')) then     print *,'Female'   else     print *,'Something went wrong' end if end program lab4

 

4.1.8   Select Case Statement

Select case statement is a simplified version of if…else…if…else statement, it helps to make the program to be more readable. Here, only a single condition is evaluated among several alternatives, the block the meets the condition is executed. That is to say, a select case statement allows a variable to be tested for equality against a list of values.

Syntax:

select case (expression)         case label_1         !statement       case label_2         !statement       case label_3         !statement       case default          !statement         end select

4.1.9   Lab 5 – program to test a user's gender. Modification of Lab4 program example

Fortran

program lab5   !declare variable character :: gender   !user action (what user should do) and accept input print *, 'Enter m/f to select your gender' read*, gender   !test and display output    select case (gender)       case ('m')         print*, 'Male'       case ('M')         print*, 'Male'       case ('f')         print*, 'Female'       case ('F')         print*, 'Female'       case default          print*, 'Something went wrong'    end select      print*, "Your gender is:: ", gender end program lab5