ExpressionParser::ExpressionParser(const String & expression)
{
_tokens.clear();
_prefixTokens.clear();
tokenize(fixClosingBrackets(expression));
shuntingYard();
}
/* returns 0. */
float eval(float x, float y, int& errval) {
stack<float> values; // Stack of values to be evaluated
float operands[2]; // Array to contain the two operands (assuming n=2 arguments for any operator)
string s_vars[2]={ftos(x), ftos(y)}; // Store x and y in one array for easy iteration
for(int thisvar=0; thisvar<2; thisvar++) // Substitute for each variable
{
vector<string> vec_var=shuntingYard(s_vars[thisvar]);
cout << "Substituting variable... " << vtos(vec_var) << endl;
// Go through vector, inserting 'x' or 'y' into all instances of variable
for(int i=0; i<expression.size(); i++) {
if(expression[i]==rel_var[thisvar]) {
expression.erase(expression.begin()+i);
expression.insert(expression.begin()+i, vec_var.begin(), vec_var.end());
i+=vec_var.size();
}
}
}
cout << "After substitution: " << vtos(expression) << endl; // Debugging stuff, displays result
cout << "Parsing tokens..." << endl;
for(int i=0; i<expression.size(); i++) {
string token=expression[i];
// If it's a number, push it to the stack
if(isdigit(token[0]))
values.push(atof(token.c_str()));
// If it's an operator, evaluate
else if(searchFor(token, operators, NUM_OPS)) {
float result;
if(values.size()<2) { // Not enough values
errval=INSUFF;
return 0.0;
}
operands[1]=values.top();
values.pop();
operands[0]=values.top();
values.pop();
// Evaluate the operator
switch(token[0]) {
case '.':
result=operands[0]+operands[1]/pow(10, numDigits(operands[1]));
cout << operands[1] << endl;
break;
case '^':
if(operands[0]<0) {
errval=IMAGINARY;
return 0.0;
}
result=pow(operands[0], operands[1]);
break;
case '*':
result=operands[0]*operands[1];
break;
case '/':
if(operands[1]==0) {
errval=DIVZERO;
return 0.0;
}
result=operands[0]/operands[1];
break;
case '+':
result=operands[0]+operands[1];
break;
case '-':
result=operands[0]-operands[1];
break;
default:
errval=OPER;
return 0.0;
}
values.push(result);
}
else {
errval=OPER;
return 0.0;
}
}
if(values.size()==1) { // That one value is the result
errval=NONE;
return values.top();
}
else { // Problem, too many values on stack
errval=VAL;
return 0.0;
}
}
ExpressionParser::ExpressionParser(const std::string & expression)
{
tokenize(fixClosingBrackets(expression));
shuntingYard();
}
