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#include <iostream>
#include <fstream>
#include <stack>
#include <string>
using namespace std;
class Expression{
public:
string inToPost();
string inToPre();
string postToIn();
string preToIn();
string convertThis; // Expression that we want converted
double evaluate(); // Evaluate expression
Expression(string input, int direction); //constructor
bool isOperator(char character);
bool isOperand(char character);
int isHigherWeight(char character);
bool isHigherPrecedence(char op1, char op2);
void printResult();
private:
string infix;
string postfix;
string prefix;
};
//Constructor function
Expression::Expression(string input, int direction){
switch (direction){
case 1: infix = input;
case 2: postfix = input;
case 3: prefix = input;
}
}
//Operator Function checks to see if character is a legal symbol
bool Expression::isOperator(char character){
if((character == '*')||(character == '+')||(character == '-')||(character == '/'))
return true;
else
return false;
}
//Operand Function checks to see if character is a legal character
bool Expression::isOperand(char character){
if(character >= 'a' && character <= 'z')
return true;
if(character >= 'A' && character <= 'Z')
return true;
if(character >= '0' && character <= '9')
return true;
else
return false;
}
//Function determines the weight of Operator.
int Expression::isHigherWeight(char character){
int weight = 0; // or -1?
switch(character){
case '+':
case '-':
weight = 1;
case '*':
case '/':
weight = 2;
}
return weight;
}
//Function that compares weights of two different Operators.
bool Expression::isHigherPrecedence(char oper1, char oper2){
int op1Weight = isHigherWeight(oper1);
int op2Weight = isHigherWeight(oper2);
// If operators have equal precedence, return true
// return false
return op1Weight > op2Weight ? true: false;{
}
}
string Expression::inToPost(){
/** ->Initialize a stack of characters to hold the operation symbols and parentheses
-> do
if(the next input is a left parenthesis)
1-Read the left parenthesis and push it onto the stack
2-else if( the next input is a number or other operand)
3-Read the operand and write it to the output
4-else if( the next input is one of the operation symbols)
5-Print the top operation and pop it
**/
stack<char> Stack;
string postfix = ""; // Initialize postfix as empty string.
for(int i = 0;i< convertThis.length();i++){ //go through array of string convertThis
if (convertThis[i] == '('){ //1-Read the left parenthesis and push it onto the stack
Stack.push(convertThis[i]);
}
else if(isOperand(convertThis[i])){ //2-else if( the next input is a number or other operand)
cout << convertThis[i]; //3-Read the operand and write it to the output
}
else if(isOperator(convertThis[i])){ //4-else if the next input is one of the operation symbols)
cout << Stack.top();
Stack.pop(); //5-Print the top operation and pop it
}
/**
(while none of these three conditions are true){
6- The stack becomes empty, or
- The next symbol on the stack is a a left parenthesis, or
- The next symbol on the stack is an operation with lower precedence than the next input symbol
7- Read the next input symbol, and push this symbol onto the stack
}
else **/ //6-
while(!Stack.empty() && Stack.top() != '(' && isHigherPrecedence(Stack.top(),convertThis[i])){
Stack.push(convertThis[i]); //7- Read the next input symbol, and push this symbol onto the stack
}
/**
8- Read and discard the next input symbol(which should be a right parenthesis).
9- Print the top operation and pop it; Keep printing and popping until
- the next symbol on the stack is a left parenthesis.(If no parenthesis
- is encountered, then print an error message indicating unbalanced
- parentheses, and halt.)
10- Finally, pop the left parenthesis.
**/
// 8- Read and discard the next input symbol(which should be a right parenthesis).
if (convertThis[i] == ')'){
// 9- Print the top operation and pop it; Keep printing and popping until
while (!Stack.top() == '('){
cout << Stack.top();
Stack.pop();
}
}
Stack.pop(); //10- Finally, pop the left parenthesis.
/**while(there is more of the expression to read);
11- Print and pop any remaining operations on the stack.
(There should be no remaining left parentheses; if there are,
the input expression did not have balanced parentheses.)
**/
while(!Stack.empty()){
cout << Stack.top();
}
return postfix;
cout << postfix;
}
}
string Expression::inToPre(){
}
string Expression::postToIn(){
}
string Expression::preToIn(){
}
double Expression::evaluate(){
}
void Expression::printResult(){
cout << inToPost();
}
int main(){
string convertThis;
int choice;
cout << "|-----Here is my conversion menu-----|" << endl;
cout << "|----What are you converting to?-----|" << endl << endl;
cout << "1- Infix to postfix" << endl;
cout << "2- Infix to prefix" << endl;
cout << "3- postfix to infix?" << endl;
cout << "4- prefix to infix?" << endl;
//cin >> choice;
//cin.ignore();
cout << "Now enter the expression you want to convert ";
getline(cin,convertThis);
printResult();
}
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