Rexx - Decision Making


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Decision making structures require that the programmer specify one or more conditions to be evaluated or tested by the program.

The following diagram shows the general form of a typical decision-making structure found in most of the programming languages.

Decision Making

There is a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Let’s look at the various decision-making statements available in Rexx.

S.No. Statement & Description
1 If statement

The first decision-making statement is the if statement. An if statement consists of a Boolean expression followed by one or more statements.

2 If-else statement

The next decision-making statement is the if-else statement. An if statement can be followed by an optional else statement, which executes when the Boolean expression is false.

Nested If Statements

Sometimes there is a requirement to have multiple if statements embedded inside each other, as is possible in other programming languages. In Rexx also this is possible.

Syntax

if (condition1) then 
   do 
      #statement1 
   end 
else 
   if (condition2) then 
      do 
      #statement2 
   end

Flow Diagram

The flow diagram of nested if statements is as follows −

Nested If Statement

Let’s take an example of nested if statement −

Example

/* Main program */ 
i = 50 
if (i < 10) then 
   do 
      say "i is less than 10" 
   end 
else 
if (i < 7) then 
   do 
      say "i is less than 7" 
   end 
else 
   do 
      say "i is greater than 10" 
   end 

The output of the above program will be −

i is greater than 10 

Select Statements

Rexx offers the select statement which can be used to execute expressions based on the output of the select statement.

Syntax

The general form of this statement is −

select 
when (condition#1) then 
statement#1 

when (condition#2) then 
statement#2 
otherwise 

defaultstatement 
end 

The general working of this statement is as follows −

  • The select statement has a range of when statements to evaluate different conditions.

  • Each when clause has a different condition which needs to be evaluated and the subsequent statement is executed.

  • The otherwise statement is used to run any default statement if the previous when conditions do not evaluate to true.

Flow Diagram

The flow diagram of the select statement is as follows

Select Statement

The following program is an example of the case statement in Rexx.

Example

/* Main program */ 
i = 50 
select 
when(i <= 5) then 
say "i is less than 5" 

when(i <= 10) then 
say "i is less than 10" 

otherwise 
say "i is greater than 10" 
end

The output of the above program would be −

i is greater than 10 


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