help with prog3_2.lua pls prog3_2.lua In Lua, implement the Infix to Postfix fun

Question

help with prog3_2.lua pls

prog3_2.lua In Lua, implement the Infix to Postfix function that went over in class. The function

InfixToPostfix(str) takes a single argument (it will be an input string). To

kenize that input string

by space (split by space) and then apply the infix to postfix algorithm to return a postfix string.

prog3_3.cpp will be written in C/C++. It will be called prog3_3.cpp and can/should be an

extension of prog3_1.cpp The program will create a lua environment, load/run the file specified

by the command line argument. It will then take in a line of input from the stdin, call the

InfixToPostfix() function in lua (use the dostring), retrieve the resulting postfix string from the

lua stack (use the checkstring function) and then print the resultant postfix string.

this program is called prog3_3.cpp which complies but I am having trouble how to write a InfixToPostfix() function in lua help pls!

#include <lua.hpp>
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
#include <iostream>
#include <string>
#include <cstring>
#include <stdlib.h>
using namespace std;
int main(int argc, char * argv[]){
    string buffer, infix;
    const char *finalstring;
    lua_State *L = luaL_newstate();
    luaL_openlibs(L);
    luaL_dofile(L,argv[1]);
    getline(cin,buffer);
    lua_getglobal(L,"InfixtoPostfix");
    lua_pushstring(L,buffer.c_str());
    finalstring = lua_tostring(L, -1);
    cout << finalstring << endl;
    lua_close(L);
    return 0;
}

Explanation / Answer

--[[ Stack

A Simple Stack in Lua

Functions:

* push

* pop

* peek

* isEmpty

]]--

Stack = {}

Stack.__index = Stack

function Stack.new()

return setmetatable({}, Stack)

end

function Stack:push(input)

self[#self+1] = input

end

function Stack:pop()

if self:isEmpty() then

return -1

end

local tmp = self[#self]

self[#self] = nil

return tmp

end

function Stack:peek()

if self:isEmpty() then

return -1

end

return self[#self]

end

function Stack:isEmpty()

return #self == 0

end

function Stack:size()

return #self

end

--[[

--Testing the Stack

local s = Stack.new()

print(s:isEmpty()) -- {}

s:push(1) -- {1}

s:peek() -- {1}

print(s:isEmpty()) -- {1}

s:push(5) -- {1, 5}

s:push(10) -- {1, 5, 10}

print(s:pop()) -- {1, 5}

print(s:pop()) -- {1}

s:push(20) -- {1, 20}

print(s:pop()) -- {1}

print(s:pop()) -- {}

print(s:isEmpty()) -- {}

]]--

function prec(ch) --precedence

if ch == '+' or ch == '-' then

return 1

elseif ch == '*' or ch == '/' or ch == '%' then

return 2

elseif ch == '^' then

return 3

end

return -1

end

function infixToPostfix(input)

local result = ""

local oppStack = Stack.new()

--for token in string.gmatch(input, "%S+") do --gets rid of spaces

for i = 1, #input do

local token = input:sub(i,i)

--print("token: " .. token .. " precedence: " .. prec(token) .. " result: " .. result .. " stack size: " .. oppStack:size())

if prec(token) ~= -1 then --operator (+,-,*,/,%,^)

print("operator " .. token)

print(oppStack.size)

while not oppStack:isEmpty() and prec(token) <= prec(oppStack:peek()) do

print("poppin")

result = result .. oppStack:pop()

oppStack:push(token) --oops didnt have this

end

--[[

elseif token == '(' then

--print("start parentheses " .. token)

oppStack:push(token)

elseif token == ')' then

--print("end parentheses " .. token)

while not oppStack:isEmpty() and oppStack:peek() ~= '(' do

result = result .. oppStack:pop()

end

if not oppStack:isEmpty() and oppStack:peek() ~= '(' then

return "invalid parentheses"

else

oppStack:pop()

end

--]]

else --opperand (a,b,c,1,2,3)

--print("operand " .. token)

result = result .. token

end

end

while not oppStack:isEmpty() do

result = result .. oppStack:pop()

end

return result

end

function test()

print(infixToPostfix("a+b*(c^d-e)^(f+g*h)-i"))

--should print abcd^e-fgh*+^*+i-

end

test()

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