Explain this C++ code please #include #include #include

Explain this C++ code please #include <vector> #include <iostream> #include <fst

ID: 3740817 • Letter: E

Question

Explain this C++ code please

#include <vector>

#include <iostream>

#include <fstream>

#include <stdexcept>

#include <string>

#include <cctype>

#include <bitset>

#include <algorithm>

using namespace std;

class Lable {

public:

int romAddress;

int position;

string lable;

Lable(int a, int b, string c):romAddress(a), position(b), lable(c){};

};

//get each line

void handle(vector<string>& t, string& s, int& counter, vector<Lable>& flag) {

string str_dest = "xxx";

string str_jump = "xxx";

string str_comp = "xxxxxxx";

//delete comments and whitespaces

s = s.substr(0,s.find("//"));

s.erase(remove_if(s.begin(), s.end(), [&] (char c){return isspace(static_cast<unsigned char>(c));}),s.end());

while(!s.empty()) {

//deal with (LABLE)

if(s[0] == '(') {

s.erase(s.begin());

s = s.substr(0,s.find(")"));

for(int j = 0; j < flag.size(); j++) {

if(s.compare(flag[j].lable)==0) {

flag[j].position = counter;

return;

}

Lable at(-1, counter, s);

flag.push_back(at);

return;

}

//deal with A-Instruction

else if(s[0] == '@') {

s.erase(s.begin());

//Predefined Symbols

if(s.compare("SP")==0) t.push_back("0000000000000000");

else if(s.compare("LCL")==0) t.push_back("0000000000000001");

else if(s.compare("ARG")==0) t.push_back("0000000000000010");

else if(s.compare("THIS")==0) t.push_back("0000000000000011");

else if(s.compare("THAT")==0) t.push_back("0000000000000100");

else if(s.compare("SCREEN")==0) t.push_back("0100000000000000");

else if(s.compare("KBD")==0) t.push_back("0110000000000000");

else if(s.compare("R0")==0) t.push_back("0000000000000000");

else if(s.compare("R1")==0) t.push_back("0000000000000001");

else if(s.compare("R2")==0) t.push_back("0000000000000010");

else if(s.compare("R3")==0) t.push_back("0000000000000011");

else if(s.compare("R4")==0) t.push_back("0000000000000100");

else if(s.compare("R5")==0) t.push_back("0000000000000101");

else if(s.compare("R6")==0) t.push_back("0000000000000110");

else if(s.compare("R7")==0) t.push_back("0000000000000111");

else if(s.compare("R8")==0) t.push_back("0000000000001000");

else if(s.compare("R9")==0) t.push_back("0000000000001001");

else if(s.compare("R10")==0) t.push_back("0000000000001010");

else if(s.compare("R11")==0) t.push_back("0000000000001011");

else if(s.compare("R12")==0) t.push_back("0000000000001100");

else if(s.compare("R13")==0) t.push_back("0000000000001101");

else if(s.compare("R14")==0) t.push_back("0000000000001110");

else if(s.compare("R15")==0) t.push_back("0000000000001111");

//covert decimal number to binary

else if(isdigit(s[0])) {

int num = atoi(s.c_str());

t.push_back("0" + bitset<15>(num).to_string());

}

//deal with @LABLE

else {

for(int j = 0; j < flag.size(); j++) {

//find exist symbol name

if(s.compare(flag[j].lable)==0) {

if(flag[j].position!=-1 && flag[j].romAddress!=-1) {

Lable at(counter, flag[j].position, s);

flag.push_back(at);

t.push_back("XXXXXXXXXXXXXXXX");

counter++;

return;

}

//multi variable name

else if(flag[j].position==-1 && flag[j].romAddress!=-1) {

Lable at(counter, -1, s);

flag.push_back(at);

t.push_back("XXXXXXXXXXXXXXXX");

counter++;

return;

}

//get romAddress for (LABLE)

else {

flag[j].romAddress = counter;

t.push_back("XXXXXXXXXXXXXXXX");

counter++;

return;

}

//new lable

Lable at(counter, -1, s);

flag.push_back(at);

t.push_back("XXXXXXXXXXXXXXXX");

}

counter++;

return;

}

//deal with C-Instruction

else {

int equal_position = s.find_first_of('=');

int semicolon_position = s.find_first_of(';');

//dest

if(equal_position < 0) str_dest = "000";

else {

string dest = s.substr(0, equal_position);

if(dest.compare("M")==0) str_dest = "001";

else if(dest.compare("D")==0) str_dest = "010";

else if(dest.compare("MD")==0) str_dest = "011";

else if(dest.compare("A")==0) str_dest = "100";

else if(dest.compare("AM")==0) str_dest = "101";

else if(dest.compare("AD")==0) str_dest = "110";

else if(dest.compare("AMD")==0) str_dest = "111";

}

//jump

if(semicolon_position < 0) str_jump = "000";

else {

string jump = s.substr(semicolon_position+1, s.length()-semicolon_position-1);

if(jump.compare("JGT")==0) str_jump = "001";

else if(jump.compare("JEQ")==0) str_jump = "010";

else if(jump.compare("JGE")==0) str_jump = "011";

else if(jump.compare("JLT")==0) str_jump = "100";

else if(jump.compare("JNE")==0) str_jump = "101";

else if(jump.compare("JLE")==0) str_jump = "110";

else if(jump.compare("JMP")==0) str_jump = "111";

}

//comp

string comp;

if(equal_position < 0 && semicolon_position < 0) comp = s;

else if(equal_position <= s.length() && semicolon_position < 0) comp = s.substr(equal_position+1, s.length()-equal_position-1);

else if(equal_position < 0 && semicolon_position <= s.length()) comp = s.substr(0, semicolon_position);

else comp = s.substr(equal_position+1, semicolon_position-equal_position-1);

if(comp.compare("0")==0) str_comp = "0101010";

else if(comp.compare("1")==0) str_comp = "0111111";

else if(comp.compare("-1")==0 ) str_comp = "0111010";

else if(comp.compare("D")==0) str_comp = "0001100";

else if(comp.compare("A")==0) str_comp = "0110000";

else if(comp.compare("!D")==0) str_comp = "0001101";

else if(comp.compare("!A")==0) str_comp = "0110001";

else if(comp.compare("-D")==0) str_comp = "0001111";

else if(comp.compare("-A")==0) str_comp = "0110011";

else if(comp.compare("D+1")==0) str_comp = "0011111";

else if(comp.compare("A+1")==0) str_comp = "0110111";

else if(comp.compare("D-1")==0) str_comp = "0001110";

else if(comp.compare("A-1")==0) str_comp = "0110010";

else if(comp.compare("D+A")==0 ) str_comp = "0000010";

else if(comp.compare("A-D")==0) str_comp = "0000111";

else if(comp.compare("D&A")==0) str_comp = "0000000";

else if(comp.compare("D|A")==0) str_comp = "0010101";

else if(comp.compare("M")==0) str_comp = "1110000";

else if(comp.compare("!M")==0) str_comp = "1110001";

else if(comp.compare("-M")==0) str_comp = "1110011";

else if(comp.compare("M+1")==0) str_comp = "1110111";

else if(comp.compare("M-1")==0) str_comp = "1110010";

else if(comp.compare("D+M")==0) str_comp = "1000010";

else if(comp.compare("D-M")==0) str_comp = "1010011";

else if(comp.compare("M-D")==0) str_comp = "1000111";

else if(comp.compare("D&M")==0) str_comp = "1000000";

else if(comp.compare("D|M")==0) str_comp = "1010101";

t.push_back("111" + str_comp + str_dest + str_jump);

counter++;

return;

}

return;

}

//get the machine code of symbols

void symbol(vector<string>& t, vector<Lable>& flag) {

int address = 16;

for(int j = 0; j < flag.size(); j++) {

//ignore unlocated lables

if(flag[j].romAddress == -1) continue;

//get variable positions starting at ROM[16]

if(flag[j].position == -1) {

int c = 0; //flag

//variable address already took

for(int q = 0; q < j; q++){

if((flag[j].lable).compare(flag[q].lable)==0) {

c=1;

t[flag[j].romAddress] = t[flag[q].romAddress];

}

//give a new romAddress

if(c==0){

t[flag[j].romAddress] = "0" + bitset<15>(address).to_string();

address++;

}

//get LABLE positions

else {

t[flag[j].romAddress] = "0" + bitset<15>(flag[j].position).to_string();

}

int main()

try {

while(true) {

//input .asm file

cout << "File name? (Exclude '.asm')" << endl;;

string fileName = "";

cin >> fileName;

string fileNameAsm = fileName + ".asm";

ifstream ist (fileNameAsm);

if (!ist) throw string("Can't open file.");

string s = "";

vector<string> t;

vector<Lable> flag;

int counter = 0;

//get each line

while(getline(ist,s)) {

handle(t,s,counter,flag);

}

symbol(t,flag);

//creat .hack file

string fileNameHack = fileName + ".hack";

ofstream ost (fileNameHack);

for(int i = 0; i < t.size(); i++) {

ost << t[ i] << endl;

}

cout << "Successful conversion. Lines:" << t.size() << endl;

}

return 0;

}

catch(string& e) {

cerr << "error: " << e << ' ';

return 1;

}

catch(exception& e) {

cerr << "error: " << e.what() << ' ';

return 2;

}

catch(...) {

cerr << "Unknown exception! ";

return 3;

}

Explanation / Answer