Lua - if...else statement

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

Syntax - if...else statement

The syntax of an if...else statement in Lua programming language is −

if(boolean_expression)
then
   --[ statement(s) will execute if the boolean expression is true --]
else
   --[ statement(s) will execute if the boolean expression is false --]
end

If the Boolean expression evaluates to true, then the if block of code will be executed, otherwise else block of code will be executed.

Lua programming language assumes any combination of Boolean true and non-nil values as true, and if it is either Boolean false or nil, then it is assumed as false value. It is to be noted that in Lua, zero will be considered as true.

Flow Diagram

Example - Usage of if...else statement

In this example, we're showing the usage of if else statement. We've created a variable a and initialized it to 100. Then in the if statement, we're checking x with 20. As if statement is false, the statement within the else block is executed.

main.lua

--[ local variable definition --]
a = 100;

--[ check the boolean condition --]

if( a < 20 )
then
   --[ if condition is true then print the following --]
   print("a is less than 20" )
else
   --[ if condition is false then print the following --]
   print("a is not less than 20" )
end

print("value of a is :", a)

Output

When you build and run the above code, it produces the following result.

a is not less than 20
value of a is :	100

The if...else if...else Statement

An if statement can be followed by an optional else if...else statement, which is very useful to test various conditions using single if...else if statement.

While using if , else if , else statements, there are a few points to keep in mind −

• An if can have zero or one else's and it must come after any else if's.

• An if can have zero to many else if's and they must come before the else.

• Once an else if succeeds, none of the remaining else if's or else's will be tested.

Syntax - if...elseif...else statement

The syntax of an if...else if...else statement in Lua programming language is −

if(boolean_expression 1)
then
   --[ Executes when the boolean expression 1 is true --]

elseif( boolean_expression 2)
   --[ Executes when the boolean expression 2 is true --]

elseif( boolean_expression 3)
   --[ Executes when the boolean expression 3 is true --]
else 
   --[ executes when the none of the above condition is true --]
end

Example - Usage of if...else if...else Statement

In this example, we're showing the usage of if...else if...else statement. We've created a variable a and initialized it to 10. Then in the if statement, we're checking a with 10. As if statement is false, control jumps to else if statement checking another value with a and so on.

main.lua

--[ local variable definition --]
a = 100

--[ check the boolean condition --]

if( a == 10 )
then
   --[ if condition is true then print the following --]
   print("Value of a is 10" )
elseif( a == 20 )
then   
   --[ if else if condition is true --]
   print("Value of a is 20" )
elseif( a == 30 )
then
   --[ if else if condition is true  --]
   print("Value of a is 30" )
else
   --[ if none of the conditions is true --]
   print("None of the values is matching" )
end
print("Exact value of a is: ", a )

Output

When you build and run the above code, it produces the following result.

None of the values is matching
Exact value of a is:	100

The nested if-else Statement

The nested if else statement is used for better decision-making when other conditions are to be checked when a given condition is true. In the nested if else statement, you can have an if-else statement block the another if (or, else) block.

Syntax - nested if else Statement

The syntax of a nested if-else statement in Lua programming language is −

if(condition1)  
then
	-- code block    
	if(condition2)
    then	
		-- code block 
    end
end

Example - Nested if...else statement

The following examples finds the largest number among three using nested if..else statement.

main.lua

x, y, z = 10, 20, 30
if (x >= y)
then
   if(x >= z)
   then
      print(x, " is the largest.")
   else
      print(z, " is the largest.")
   end
else
   if(y >= z)
   then
       print(y, " is the largest.")
   else
       print(z, " is the largest.")
   end
end

Output

When you build and run the above code, it produces the following result.

30	 is the largest.