Lua expressions and control structures Learning notes _node.js

Arithmetic operator

The arithmetic operators in Lua are:

"+" (addition):

Copy Code code as follows:

Print (1 + 2)

"-" (subtraction):

Copy Code code as follows:

Print (2-1)

"*" (multiplication):

Copy Code code as follows:

Print (1 * 2)

"/" (division):

Copy Code code as follows:

Print (1/2)

"^" (index):

Copy Code code as follows:

Print (27^ ( -1/3))

"%" (modulo):

Copy Code code as follows:

Print (5% 3)

Relational operators

Lua provides the following relational operators:

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< > <= >= = = ~=

The result of the operation returned by the above operator is either true or false. Strings and numbers cannot be compared

logical operators

Logical operators have and, or, not

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Print (1 and 2)
Print (nil and 1)
Print (FALSE and 2)
Print (1 or 2)
Print (False or 5)

The logical operator treats false and nil as false, others as true.

Local Variables and scopes

Lua creates local variables by means of a local statement whose scope is limited to the block that declares them.

Copy Code code as follows:

Local A, B = 1, 10
If a < b then
Print (a)
Local A
Print (a)
End
Print (A, B)

Saving global variables with local variables can speed up access to global variables in the current scope. For the effect of acceleration, compare the following calculations for the execution time of the Fibonacci sequence (Fibonacci):

Copy Code code as follows:

function Fibonacci (N)
If n < 2 Then
return n
End
Return Fibonacci (N-2) + Fibonacci (n-1)
End
Io.write (Fibonacci), "\ n")

Use local variables

Copy Code code as follows:

Local function Fibonacci (n)
If n < 2 Then
return n
End
Return Fibonacci (N-2) + Fibonacci (n-1)
End
Io.write (Fibonacci), "\ n")

Control structure

If then ElseIf else end

Copy Code code as follows:

if num = = 1 Then
Print (1)
ElseIf num = = 2 Then
Print (2)
Else
Print ("other")
End

Lua does not support switch statements

While

First judge the while condition, if the condition is true, follow the execution loop body, or end

Copy Code code as follows:

Local i = 1
While A[i] do
Print (A[i])
i = i + 1
End

Repeat-until

Execute the loop body first, then judge the condition, if the condition is true, exit the loop body, otherwise continue to execute the loop body. Do-while statements similar to other languages, the loop body will execute at least once

Copy Code code as follows:

Local A = 1
Repeat
A = a + 1
b = A
Print (b)
Until B < 10

For loop

There are two forms of a For Loop statement: Numeric for (numeric for), generic for (generic for)

Numeric for syntax:

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For start and end
Doing something
End

Start is the starting value, end is the ending value, and step is stride (optional, default is 1)

Copy Code code as follows:

For a = ten, 0,-2 do
Print (a)
End

The generic for loop traverses all values through an iterator (iterator) function:

Copy Code code as follows:

tab = {Key1 = "val1", Key2 = "Val2", "Val3"}
For K, V in Pairs (tab) do
if k = = "Key2" Then
Break
End
Print (K.. " - " .. V
End

Break and return statements are used to jump out of the currently executing block.