void IfStmt::execute(EvalState & state) {
if(op == "=") {
if (lhsExp->eval(state) == rhsExp->eval(state)) {
state.setCurrentLine(lineNumber);
}
} else if (op == ">") {
if(lhsExp->eval(state) > rhsExp->eval(state))
state.setCurrentLine(lineNumber);
} else {
if(lhsExp->eval(state) < rhsExp->eval(state))
state.setCurrentLine(lineNumber);
}
}
void processLine(string line, Program & program, EvalState & state) {
TokenScanner scanner;
scanner.ignoreWhitespace();
scanner.scanNumbers();
scanner.setInput(line);
string str=scanner.nextToken();
if (scanner.getTokenType(str)==NUMBER) {
int lineNumber=stringToInteger(str);
string token=scanner.nextToken();
scanner.saveToken(token);
if (token!="") {
program.addSourceLine(lineNumber, line);
program.setParsedStatement(lineNumber, parseStatement(scanner));
}
else {
program.removeSourceLine(lineNumber);
}
}
else if (str=="LIST") {
for (int i=program.getFirstLineNumber(); i!=-1; i=program.getNextLineNumber(i)) {
cout << program.getSourceLine(i)<<endl;
}
}
else if (str=="CLEAR") {
program.clear();
}
else if(str=="QUIT") exit(0);
else if (str=="HELP") cout<<"This is a minimal BASIC interpreter."<<endl;
else if (str=="RUN") {
int currentLine=program.getFirstLineNumber();
state.setCurrentLine(currentLine);
while (currentLine!=-1) {
program.getParsedStatement(currentLine)->execute(state);
if(currentLine!=state.getCurrentLine()) {
currentLine=state.getCurrentLine();
}
else {
currentLine=program.getNextLineNumber(currentLine);
state.setCurrentLine(currentLine);
}
}
}
}
void IfStmt::execute(EvalState &state) {
if (op == "=") {
if (lhs->eval(state) == rhs->eval(state))
state.setCurrentLine(nextLine);
}
else if (op == ">") {
if (lhs->eval(state) > rhs->eval(state))
state.setCurrentLine(nextLine);
}
else if (op == "<") {
if (lhs->eval(state) < rhs->eval(state))
state.setCurrentLine(nextLine);
}
}
void runProgram(Program & program, EvalState & state) {
int lineNumber = program.getFirstLineNumber();
while (lineNumber != -1) {
Statement * stmt = program.getParsedStatement(lineNumber);
state.setCurrentLine(program.getNextLineNumber(lineNumber));
stmt->execute(state);
lineNumber = state.getCurrentLine();
}
}
void EndStmt::execute(EvalState & state) {
state.setCurrentLine(-1);
}
void GotoStmt::execute(EvalState & state) {
state.setCurrentLine(line);
}
/*
* Function: processLine
* Usage: processLine(line, program, state);
* -----------------------------------------
* Processes a single line entered by the user. In this version,
* the implementation does exactly what the interpreter program
* does in Chapter 19: read a line, parse it as an expression,
* and then print the result. In your implementation, you will
* need to replace this method with one that can respond correctly
* when the user enters a program line (which begins with a number)
* or one of the BASIC commands, such as LIST or RUN.
*/
void processLine(string line, Program & program, EvalState & state) {
TokenScanner scanner;
scanner.ignoreWhitespace();
scanner.scanNumbers();
scanner.setInput(line);
string token=scanner.nextToken();
TokenType type=scanner.getTokenType(token);
int lineNumb;
int priorLineNumb;
if(type==NUMBER){
if(scanner.hasMoreTokens()){
program.addSourceLine(stringToInteger(token),line);
Statement *stmt=parseStatement(scanner);
program.setParsedStatement(stringToInteger(token),stmt); //link statement to line number
}
else
program.removeSourceLine(stringToInteger(token));
}
if(type==WORD){
if(token=="LIST"){
lineNumb=program.getFirstLineNumber();
while(lineNumb!=-1){
cout<<program.getSourceLine(lineNumb)<<endl;
lineNumb=program.getNextLineNumber(lineNumb);
}
}
else if(token=="RUN"){
state.setCurrentLine(program.getFirstLineNumber());
lineNumb=state.getCurrentLine();
while(lineNumb!=-1){
if(program.hasLineNumber(lineNumb)==false)
error("Invalid line reference at program line "+integerToString(priorLineNumb));
Statement *stmt=program.getParsedStatement(lineNumb);
state.setCurrentLine(program.getNextLineNumber(lineNumb));
stmt->execute(state);
priorLineNumb=lineNumb;
lineNumb=state.getCurrentLine();
}
}
else if(token=="CLEAR"){
program.clear();
}
else if(token=="HELP"){
cout<<"Minimal Basic Statements"<<endl;
cout<<"REM This statement used for comments"<<endl;
cout<<"LET This statement is BASIC's assigment statement"<<endl;
cout<<"PRINT In minimal BASIC, the PRINT statement has the form: "<<endl;
cout<<" PRINT exp"<<endl;
cout<<" where exp is an expression."<<endl;
cout<<"INPUT In the minimal version of the BASIC interpreter, the INPUT statement has the form:"<<endl;
cout<<" INPUT var"<<endl;
cout<<" where var is a variable read in from the user"<<endl;
cout<<"GOTO This statement has the syntax"<<endl;
cout<<" GOTO n"<<endl;
cout<<" which forces the program to continue from line n instead of continuing with the next statement"<<endl;
cout<<"IF This statement provides conditional control. The syntax for this statement is: "<<endl;
cout<<" IF exp1 op exp2 THEN n"<<endl;
cout<<" where exp1 and exp2 are expressions and op is one of the conditional operators =, <, or >."<<endl;
cout<<"END This statment marks the end of the program."<<endl;
cout<<"Commands to control the BASIC interpreter"<<endl;
cout<<"RUN This command starts program execution beginning at the lowest-numbered line. "<<endl;
cout<<"LIST This command lists the steps in the program in numerical sequence."<<endl;
cout<<"CLEAR This command deletes the program so the user can start entering a new one."<<endl;
cout<<"HELP This command provides a simple help message describing the interpreter."<<endl;
cout<<"QUIT Typing QUIT exits from the BASIC interpreter by calling exit(0)."<<endl;
}
else if(token=="QUIT"){
exit(0);
}
else
cout<<"Invalid command"<<endl;
}
}