Decisions

Decision making statements are used to run one set of statements or another set of statements based on some conditions.

If statement:

Let’s use ruby scripts. Type notepad filename.rb. This prompts to create a new file, type yes. You can also other text editors as per you liking.

#if comparison (relational expression)
#   statements
#end

grade = gets
grade = Integer(grade)
if grade >= 70
puts "pass"
end

This is the code snippet of the program. Any statements that begins with # sign are comments. They are non-executable statements and are used for better understanding of a program.

Syntax of If statement:

if (condition)
statements
end

If the condition is true, then the statements inside if block are executed.

When running the program, it prompts the user to enter grade and it is converted to Integer. If grade entered is greater than 70 then it displays “pass”.

if conditional statement example in Ruby

You can see, when the value greater than 70 is entered, it displayed pass. If a value less than 70 is entered it displays nothing. To handle this, we need another type of statement called If - else.

If else statement:

If else statements execute one set of statements if the condition is true or another set of statements if the condition is false.

Syntax of If- else statement:

if (condition)
statements1
else
statements2
end

If the condition is true the statements inside if block is executed, if condition fails the statements inside else block are executed.

if-else conditional statement example in Ruby

If value less than 70 is entered it displays “fail”.

if-else conditional statement example in Ruby

If else statements are used for two way decisions. If we want to have more than two decisions, we can use If - Else If statement.

If - Else If Statement:

It is used to make more complex branching statements.

Syntax of If - Else If statement is

if (condition1)
statements1
elsif (condition2)
statements2
elsif (condition n)
statements3
else
statements4
end

It evaluates the condition1, if it is true it executes statements1, if the condition is false it evaluates the condtion2, if true it executes statements2 and so on. If none of the conditions is true, it executes statements4.

if-elsif-else conditional statement example in Ruby

Executing this program, prompts to enter the marks. Based on the value entered it checks the condition given in the program and displays your Grade.

if-elsif-else conditional statement example in Ruby

Case statements:

An alternate to the If - else if statement is Case statement. It is also used for making multiple decisions. We can make multiple decisions in a structured way using Case statement.

Syntax of Case statement:

case (expression)
when expression1
statements1
when expression2
statements2
else
statements3
end

Case Statement Example in Ruby

If the value of the variable grade is between 90 and 100 it assigns “A” to the variable letterGrade. Likewise, based on the input when the corresponding expression is met the following statements are executed.

Case Statement Example in Ruby