How to convert a string to int in Lua programming?

Lua does the implicit conversion or also known as coercion when it notices that you are trying to use a number but wrote a string, then it automatically converts the string into an int, and it is quite useful.

Let’s consider a simple example where I will declare a string variable, and then I will try to do an arithmetic operation on it, then once the Lua compiler infers that we are trying to use the string as an int, it will automatically convert it into an int.

Example

Consider the example shown below −

 Live Demo

str = "10"
print(type(str))
num = 2 * str
print(num)
print(type(num))

Output

string
20
number

Now that we know about the automatic conversion (coercion), it’s a good idea to learn how to do the conversion explicitly, the first approach is to append a 0 to the string value, and that value will be converted to an integer.

Example

Consider the example shown below −

 Live Demo

-- uncommon method
str = "100"
num = str + 0
print(type(num))
print(num)

Output

number
100

The above approach is not a very common one, and it's better to use the library function to convert a string to a number.

Example

Consider the example shown below −

 Live Demo

-- common method
str = "100"
num = tonumber(str)
print(type(num))
print(num)

Output

number
100