Context Free Grammer

cfg.cpp

//
//  main.cpp
//  Context-Free-Grammer
//
//  Created by Dhairya Gabhawala on 4/18/17.
//  Copyright © 2017 Dhairya Gabhawala. All rights reserved.
//

#include <iostream>
#include <string>
#include <math.h>
#include <algorithm>
using namespace std;
float x = 0,y = 0,z = 0;
int count = 0;
string expr, term, factor, id, expression, input;
float Expression(string expression),Term(string expression), Factor(string expression);

float calculate(float a, float b, char opp){
    switch (opp) {
        case '+': return a+b;
        case '-':return a-b;
        case '*':return a*b;
        case '/':return a/b;
    }
    return 0;
}

bool expoperator(char check){
    switch (check) {
        case '+': return true;
        case '-': return true;
    }
    return false;
}

bool termoperator(char check){
    switch (check) {
        case '*': return true;
        case '/': return true;
    }
    return false;
}

float Id(char expression){
    switch (expression) {
        case 'x': return x; break;
        case 'y': return y; break;
        case 'z': return z; break;
        default: break;
    }
    return 0;
}
float Factor(string expression){
    int i = expression.length()-1;
    if (expression.find('(') < expression.find(')')){
        cout << "Factor:" << expression.substr(expression.find_first_of('(')+1, expression.find_last_of(')')-1) << endl;
        return Expression(expression.substr(expression.find_first_of('(')+1, expression.find_last_of(')')-1));
    } else if (expression[i] == 'x' || expression[i] == 'y' || expression[i] =='z'){
        cout << "Id:" << expression[i] << endl;
        return Id(expression[i]);
    }
    return 0;
}

float Term(string expression){
    int i = expression.length()-1;
    for(i = i; i >= 0; i--){
        if (expression[i] == ')'){
            i = expression.substr(0,i-1).find_first_of('(');
            if ( i == 0){ //check if closing parentheses is ever before opening parentheses
                return Factor(expression);
            }
        } else if (termoperator(expression[i])){
            cout << "Term:" << expression.substr(0,i) << endl; // Remove this
            cout << "Operator:" << expression[i]<< endl; // Remove this
            cout << "Factor:" << expression.substr(i+1,expression.length()) << endl; // Remove this
            return calculate(Term(expression.substr(0,i)), Factor(expression.substr(i+1,expression.length())), expression[i]);
            break;
        } else if ((expression.find('*') > expression.length()) && (expression.find('/') > expression.length())){
            return Factor(expression);
        }
    }
    return 0;
}

float Expression(string expression) {
    int i = expression.length() - 1;
    for (i = i; i >= 0; i--) {
        if (expression[i] == ')') {
            i = expression.substr(0, i - 1).find_first_of('(');
            if (i == 0) {
                return Term(expression);
            }
        }
        else if (expoperator(expression[i])) {
            cout << "Expression:" << expression.substr(0, i) << endl; // Remove this
            cout << "Operator:" << expression[i] << endl; // Remove this
            cout << "Term:" << expression.substr(i + 1, expression.length()) << endl; // Remove this
            return calculate(Expression(expression.substr(0, i)), Term(expression.substr(i + 1, expression.length())), expression[i]);
        }
        else if ((expression.find('+') > expression.length()) && (expression.find('-') > expression.length())) {
            if (expression[0] == '(' && expression[expression.length() - 1] == ')') {
                expression = expression.substr(1, expression.length());
            }
            return Term(expression);
        }
        else
            if (i == 0) {
                return Term(expression);
            }
    }
    return 0;
}

int main(int argc, const char * argv[]) {
    int i = 1;
    cout << "*********Context Free Grammer*********" << '\n';
    while(i > 0){
        std::getline(std::cin, input);
        if ((input.find("x") < input.length()) && (input.find("=") < input.length())) {
            x = std::stof(input.substr(input.find_last_of("=")+1,input.length()));
        } else if ((input.find("y") < input.length())&& (input.find("=") < input.length())){
            y = std::stof(input.substr(input.find_last_of("=")+1,input.length()));
        } else if ((input.find("z") < input.length()) && (input.find("=") < input.length())){
            z = std::stof(input.substr(input.find_last_of("=")+1,input.length()));
        } else if (((input.find("x") < input.length()) || (input.find("y") < input.length()) || (input.find("z") < input.length())) && (input.find("=") > input.length())){
            std::string::iterator end_pos = std::remove(input.begin(), input.end(), ' ');
            input.erase(end_pos, input.end());
            expression = input;
            cout << expression << endl;
            cout << Expression(expression) << '\n' << endl;
        }
    };
    
    return 0;
}

float Expression(string expression) {
int i = expression.length() - 1;
for (i = i; i >= 0; i--) {
if (expression[i] == ')') {
i = expression.substr(0, i - 1).find_first_of('(');
if (i == 0) {
return Term(expression);
}
}// add this here
else if (expoperator(expression[i])) {
cout << "Expression:" << expression.substr(0, i) << endl; // Remove this
cout << "Operator:" << expression[i] << endl; // Remove this
cout << "Term:" << expression.substr(i + 1, expression.length()) << endl; // Remove this
return calculate(Expression(expression.substr(0, i)), Term(expression.substr(i + 1, expression.length())), expression[i]);
}
else if ((expression.find('+') > expression.length()) && (expression.find('-') > expression.length())) {
if (expression[0] == '(' && expression[expression.length() - 1] == ')') {
expression = expression.substr(1, expression.length());
}
return Term(expression);
}
else // moved this from add this here
if (i == 0) {
return Term(expression);
}
}
return 0;
}