Chap1.lua

# Lua-Uebungen/Exercises

I finished reading/working on.

Programming in Lua, Fourth Edition
Roberto Ierusalimschy
Copyright © 2016, 2003 Roberto Ierusalimschy

About the Book
Audience
Book Structure
Other Resources
A Few Typographical Conventions
> -- program "Hello "World")
> -- program "Hello "World"
-- printing exercises
-- numbers addition
-- math.sin
--variable=a=..
Running the Examples
Acknowledgments

Part I. The Basics

Chapter 1. Getting Started

```lua
Lua 5.4.2  Copyright (C) 1994-2020 Lua.org, PUC-Rio
> print("Hello World")
Hello World
> --defines a factorial function
> function fact (n) if n == 0 then return 1 else return n fact(n-1) end end print("enter a number:") a = io.read("n") --
 reads a number print(fact(a))
stdin:1: 'end' expected near 'fact'

Chunks

 -- how to enter and exit the lua interpreter
 > script.lua
>> os.exit
> os.exit()
-- chat gpt says there is a quit() cmd in the cmd line but apparently it doesnt work.. only os.exit() works
-- in the book is exponentiation not working
--  chat gpt gives solution but also = at beginning works similar to Racket lang
> a = 3
> = a^2
9
-- math.pi / 4 not working!?
-- the equal sign
=math.pi /4
0.78539816339745
--other possibility using print and putting expression between brackets 
print(a+2)
17
-- this is not working: $ lua -i prog.lua  

-- i made a file txt and i called it lib1.lua but the code that is suggested in the book does not work even if the file is in the library folder of lua..no idea..
-- book does not say where to put the lua file.. in cmd line it suggests [C]


> lua -i prog
stdin:1: syntax error near '-'
> function norm (x, y) return (x^2 + y^2)^0.5 end function twice (x) return 2*x end
> dofile("lib1.lua") -- load your library
cannot open lib1.lua: No such file or directory
stack traceback:
        [C]: in function 'dofile'
        stdin:1: in main chunk
        [C]: in ?
 
Some Lexical Conventions
--about identifiers, lua is case sensitive but "and" is both identifier and reserved word depending on how it is written with big or small cases
--how to make comments
 --[[ ]]--
"--" in between comment space or --> 
"---[[" --ordinary second line comment
> --[[ print(10) -- no action (commented out) --]]
> --[[ print(10) --> 10 --]]
 
> a = 1
b=a*2 
a=1; b =a*2;
a=1;
b=a*2
a=1
b=a*2 -- ugly, but valid

> lua
nil
> % lua
stdin:1: unexpected symbol near '%'
> ctrl-z
stdin:1: attempt to perform arithmetic on a nil value (global 'ctrl')
stack traceback:
        stdin:1: in main chunk
        [C]: in ?
> exit
nil



 Global Variables
 
> print(b) --> nil b=10 print(b) -->10
2
> b=nil print(b) -->nil
nil
> print(b) --> nil b=10 print(b) -->10
nil
> print(b) --> nil b=10 print(b) -->10
nil
> print(b) --> nil b=10 print(b) -->10
nil
> print(b) --> nil b=10 print(b) -->10
nil
> print(b) --> nil b=10 print(b) -->10
nil
> print(b) --> nil b=10 print(b) -->10
nil

 Types and Values
 Nil
 Booleans
 
 The Stand-Alone Interpreter
 --POSIX systems interpreter
 
> math.sin(3)
0.14112000805987
> a=30
> =a
30
>

 --io.flush to finish the line with or without simicolon
--there is a predefined global variable arg to find arguments
 -- more often than not only positive indeces
 --there are also vararg expression
 
-- i ran first exercise in R by using the code provided by chat gpt. Somehow the one provided in the lua book was not working but the R code appears to be working.
 > # Define the factorial function
> fact <- function(n) {
+   if (n == 0) {
+     return(1)
+   } else if (n < 0) {
+     stop("Factorial is not defined for negative numbers.")
+   } else {
+     return(n * fact(n - 1))
+   }
+ }
> 
> # Prompt the user for input
> cat("Enter a number: ")
Enter a number: > a <- as.integer(readLines(con = stdin(), n = 1))

> # Check if the input is valid
> if (!is.na(a)) {
+   # Check for negative input
+   if (a < 0) {
+     cat("Factorial is not defined for negative numbers.\n")
+   } else {
+     cat("Factorial: ", fact(a), "\n")
+   }
+ } else {
+   cat("Please enter a valid number.\n")
+ }
Please enter a valid number.
> .1
[1] 0.1
> -1
[1] -1
> -5
[1] -5
> 100
[1] 100
>