// computer.cpp : Problem #4 Virtual Computer
//


#include <stdio.h>
#include <stdlib.h>
#include <fstream.h>
#include <math.h>
#include <string.h>
#include <ctype.h>

#define MAX_TOKENS 5
#define MAX_LINE_LENGTH 100
#define MAX_TOKEN_LENGTH 10
#define MAX_PROGRAM_LENGTH 100
#define MAX_VARS 26

class Program {
	public:
		Program();

		bool end() { return programEnd; }

		void init();
		void addLine(char line[]) { strcpy(prog[numLines++], line); }
		void executeLine();
		int readNumber(char *number);

	private:
		char prog[MAX_PROGRAM_LENGTH][MAX_LINE_LENGTH];
		char tokens[MAX_TOKENS][MAX_TOKEN_LENGTH];
		int vars[MAX_VARS];

		bool programEnd;
		bool ifStatement;

		int programName;
		int numLines;
		int currentLine;
		int currentChar;

		void resetTokens();
		void getTokens();

		void executeStart();
		void executeSet();
		void executeStore();
		void executeMult();
		void executeSub();
		void executeDiv();
		void executeAdd();
		void executePrint();
		void executeGoto();
		void executeIf();
		void executeEnd() { programEnd = true; }

};

bool readProgram(Program& currentProgram);

int main(int argc, char* argv[])
{
	Program currentProgram;

	//Continue until EOF or invalid program read
	while (readProgram(currentProgram))
		while (!currentProgram.end())
			currentProgram.executeLine();

	return 0;
}

bool readProgram(Program& currentProgram)
{
	bool programRead = false;
	bool startRead = false;
	bool validProgram = true;

	char line[MAX_LINE_LENGTH] = "";
	char firstToken[MAX_TOKEN_LENGTH] = "";
	char restOfLine[MAX_LINE_LENGTH] = "";

	currentProgram.init();

	cin >> firstToken;

	while (cin && !programRead && validProgram)
	{
		strcpy(line, firstToken);

		if (strcmp(firstToken, "START") == 0)
		{
			if (startRead)
			{
				validProgram = false;
				cout << "Program contained two START statements" << endl;
			}
			else
				startRead = true;
		}
		else if (strcmp(firstToken, "END") == 0)
		{
			if (!startRead)
			{
				validProgram = false;
				cout << "Program contained END statement before START statement" << endl;
			}
			else
				programRead = true;
		}
		else
		{
			if (!startRead)
			{
				validProgram = false;
				cout << "Program did not begin with a START statement" << endl;
			}
		}

		//If the first token is not an END statement, 
		//read in rest of line and add complete line to the program
		if (!programRead)
		{
			cin.get(restOfLine, MAX_LINE_LENGTH - strlen(line));
			strcat(line, restOfLine);
			currentProgram.addLine(line);

			//Read in firstToken of next line
			cin >> firstToken;
		}
		else
			currentProgram.addLine(line);
	}

	return validProgram && cin;
}



Program::Program()
{
	init();
}

void Program::init()
{
	currentLine = 0;
	numLines = 0;
	programEnd = false;
	ifStatement = false;

	for (int i = 0; i < MAX_VARS; i++)
		vars[i] = 0;
}

void Program::executeLine()
{
	resetTokens();
	getTokens();
	
	if (strcmp(tokens[0], "START") == 0)
		executeStart();
	else if (strcmp(tokens[0], "SET") == 0) {

		executeSet();

}
	else if (strcmp(tokens[0], "STORE") == 0)
		executeStore();
	else if (strcmp(tokens[0], "MULT") == 0)
		executeMult();
	else if (strcmp(tokens[0], "SUB") == 0) {
		executeSub();
	}
	else if (strcmp(tokens[0], "DIV") == 0)
		executeDiv();
	else if (strcmp(tokens[0], "ADD") == 0)
		executeAdd();
	else if (strcmp(tokens[0], "PRINT") == 0) {
		executePrint();
}
	else if (strcmp(tokens[0], "GOTO") == 0)
		executeGoto();
	else if (strcmp(tokens[0], "IF") == 0 && strcmp(tokens[2], "IS") == 0 && strcmp(tokens[4], "THEN") == 0)
		executeIf();
	else if (strcmp(tokens[0], "END") == 0)
		executeEnd();
	else
	{
		cout << "ERROR: invalid statement" << endl;
		cout << prog[currentLine] << endl;
		programEnd = true;
	}
}

void Program::resetTokens()
{
	for (int i = 0; i < MAX_TOKENS; i++)
		tokens[i][0] = '\0';
}

void Program::getTokens()
{
	int currentToken = 0;

	if (ifStatement)
		ifStatement = false;
	else
		currentChar = 0;

	//Continue until EOL or an if statement is encountered
	while (prog[currentLine][currentChar] != '\0' && !ifStatement)
	{
		//If not at beginning of line, go to next token
		if (currentChar)
			currentChar++;

		int currentTokenChar = 0;
		while (prog[currentLine][currentChar] != ' ' && prog[currentLine][currentChar] != '\0' && currentTokenChar < MAX_TOKEN_LENGTH)
			tokens[currentToken][currentTokenChar++] = prog[currentLine][currentChar++];

		tokens[currentToken][currentTokenChar] = '\0';
		if (currentToken == 4 && strcmp(tokens[currentToken], "THEN") == 0)
			ifStatement = true;
		currentToken++;
	}
}

int Program::readNumber(char *number)
{
    int return_value;
    int start = 0;
    char actual_number[MAX_TOKEN_LENGTH];    

    if (number[0] == '-') {
        for (int i = 1; i < (strlen(number) + 1); i++) {
		actual_number[i-1] = number[i];
	}
	return_value = -1 * atoi(actual_number);
    } else {
	return_value = atoi(number);
    }

 //cout << return_value << endl;
    return return_value;
}

void Program::executeStart()
{
	programName = readNumber(tokens[1]);
	cout << prog[currentLine++] << endl;
}

void Program::executeSet()
{
	if (!tokens[1][0] || !isalpha(tokens[1][0]))
	{
		cout << "ERROR: SET <x> <value>" << endl;
		cout << "variable should be an alpha character" << endl;
		programEnd = true;
	}
	else if (!tokens[2][0])
	{
		cout << "ERROR: SET <x> <value>" << endl;
		cout << "value should be specified" << endl;
		programEnd = true;
	}
	else
	{
		vars[tokens[1][0] - 'a'] = readNumber(tokens[2]);
		currentLine++;
	}
}

void Program::executeStore()
{
	if (!tokens[1][0] || !isalpha(tokens[1][0]) || !tokens[2][0] || !isalpha(tokens[2][0]) )
	{
		cout << "ERROR: STORE <x> <y>" << endl;
		cout << "variables should be alpha characters" << endl;
		programEnd = true;
	}
	else
		vars[tokens[1][0] - 'a'] = vars[tokens[2][0] - 'a'];
	
	currentLine++;
	
}

void Program::executeMult()
{
	if (!tokens[1][0] || !isalpha(tokens[1][0]) || !tokens[2][0] || !isalpha(tokens[2][0]) )
	{
		cout << "ERROR: MULT <x> <y>" << endl;
		cout << "variables should be alpha characters" << endl;
		programEnd = true;
	}
	else
		vars[tokens[1][0] - 'a'] = vars[tokens[1][0] - 'a'] * vars[tokens[2][0] - 'a'];
		
	currentLine++;
}

void Program::executeSub()
{
	if (!tokens[1][0] || !isalpha(tokens[1][0]) || !tokens[2][0] || !isalpha(tokens[2][0]) )
	{
		cout << "ERROR: SUB <x> <y>" << endl;
		cout << "variables should be alpha characters" << endl;
		programEnd = true;
	}
	else
		vars[tokens[1][0] - 'a'] = vars[tokens[1][0] - 'a'] - vars[tokens[2][0] - 'a'];
	
	currentLine++;
}

void Program::executeDiv()
{
	if (!tokens[1][0] || !isalpha(tokens[1][0]) || !tokens[2][0] || !isalpha(tokens[2][0]) )
	{
		cout << "ERROR: DIV <x> <y>" << endl;
		cout << "variables should be alpha characters" << endl;
		programEnd = true;

	}
	else if (vars[tokens[2][0] - 'a'] == 0)
	{

	}
	else {
		vars[tokens[1][0] - 'a'] = (int) floor(((double) vars[tokens[1][0] - 'a']) / ((double)vars[tokens[2][0] - 'a']));	
	}
	currentLine++;
}

void Program::executeAdd()
{
	if (!tokens[1][0] || !isalpha(tokens[1][0]) || !tokens[2][0] || !isalpha(tokens[2][0]) )
	{
		cout << "ERROR: ADD <x> <y>" << endl;
		cout << "variables should be alpha characters" << endl;
		programEnd = true;
	}
	else
		vars[tokens[1][0] - 'a'] = vars[tokens[1][0] - 'a'] + vars[tokens[2][0] - 'a'];

	currentLine++;
}

void Program::executePrint()
{
	if (!tokens[1][0] || !isalpha(tokens[1][0]))
	{
		cout << "ERROR: PRINT <x>" << endl;
		cout << "variable should be an alpha character" << endl;
		programEnd = true;
	}
	else
		cout << vars[tokens[1][0] - 'a'] << endl;

	currentLine++;
}

void Program::executeGoto()
{
	if (!tokens[1][0])
	{
		cout << "ERROR: GOTO <n>" << endl;
		cout << "line number should be specified" << endl;
		programEnd = true;
	}
	else
	{
		int lineNum = readNumber(tokens[1]);
		if (lineNum < 1 || lineNum > numLines)
		{
			cout << "ERROR: GOTO <n>" << endl;
			cout << "line number should be a valid program line" << endl;
			cout << "numLines is " << numLines << endl;
		}	
		else
			currentLine = lineNum - 1; //offset for first line being 1
	}
}

void Program::executeIf()
{
	if (!tokens[1][0] || !isalpha(tokens[1][0]))
	{
		cout << "ERROR: IF <x> IS <value> THEN <simple_command>" << endl;
		cout << "variable should be an alpha character" << endl;
		programEnd = true;
	}
	else if (!tokens[3][0])
	{
		cout << "ERROR: IF <x> IS <value> THEN <simple_command>" << endl;
		cout << "value should be specified" << endl;
		programEnd = true;
	}
	else
	{
		if (vars[tokens[1][0] - 'a'] == readNumber(tokens[3]))
			executeLine();
		else
		{
			ifStatement = false;
			currentLine++;
		}
	}
}