Lua - Numeric Iterators

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In Lua, there are two types of for loops −

• the numeric for

• the generic for

Numeric for provides a great way to iterate through an array using indexes. We can create any sequence in ascending or descending order. We can navigate an array as well using numeric for. In this article, we'll explore various use cases of numeric for based iteration using multiple examples.

Syntax

The numeric for uses the following syntax −

for var=exp1,exp2,exp3 do
   something
end

It should be noted that we can write exp1, exp2, exp3 at the same time or we can omit one of them, and the numeric loop will not result in a compile error, though its functionality will change.

Example - Create Sequence in Ascending Order

Let's consider a simple variation of a numeric for loop, where we will try to print numbers from 1 to 10.

main.lua

Consider the example shown below −

for i = 1, 10 do
   print(i)
end

Output

When the above code is built and executed, it produces the following result −

1
2
3
4
5
6
7
8
9
10

Okay, that was simple! How about printing the numbers in a backward order? In that case, we need the exp3 that was mentioned in the syntax of the numeric for loop.

Example - Create Sequence in Descending Order

Consider the example shown below which will print the numbers from 10 to 1.

main.lua

for i = 10, 1, -1 do
   print(i)
end

Output

When the above code is built and executed, it produces the following result −

10
9
8
7
6
5
4
3
2
1

Now, let's explore a more common and useful case, where we want to iterate over an array in Lua, and print the values that are present inside the array.

Example - Traversing an Array of Strings

Consider the example shown below −

main.lua

names = {"John", "Joe", "Steve"}
for i = 1, 3 do
   print(names[i])
end

Output

When the above code is built and executed, it produces the following result −

John
Joe
Steve