Infix to Post expression | Postfix expression evaluation | C++

infix_to_postfix_main.cpp

#include <iostream>
#include <stack>
#include <cmath>
using namespace std;
// precedence of each operator
bool precedence(char stack_top, char strin){
	if(strin=='-'){
		if(stack_top=='+' or stack_top=='*' or stack_top=='/' or stack_top=='^'){
			return(true);
		}
	}
	if(strin=='+'){
		if(stack_top=='-' or stack_top=='*' or stack_top=='/' or stack_top=='^'){
			return(true);
		}
	}else if(strin=='*'){
		if(stack_top=='/' or stack_top=='^'){
			return(true);
		}
	}else if(strin=='/'){
		if(stack_top=='^'){
			return(true);
		}
	}
	return(false);

}
string postfix(string exp){
	stack<char> s;
	s.push('$'); //initial item in stack
	string res=""; // stores postfix expression of infix expression
	for(int i=0;i<exp.length();i++){
		if(exp[i]>='1' and exp[i]<='9'){
			res+=exp[i];

		}else if(exp[i]=='('){ // if exp[i]=='(', just push it into the stack
			s.push(exp[i]);

		}else if(exp[i]==')'){
			while(s.top()!='$' and s.top()!='('){
				char c=s.top();
				res=res+c;
				s.pop();
			}
			if(s.top()=='('){
				char c=s.top();
				s.pop();
			}

		}
		else{
			while(s.top()!='$' and precedence(s.top(), exp[i])){
				res=res+s.top();
				s.pop();
			}
			s.push(exp[i]);
		}

	}
	// if there are any more items in the stack, then pop them and append them into res
	while(s.top()!='$'){
		res+=s.top();
		s.pop();
	}
	return(res);
}
int process(int x, int y, char c){
	if(c=='+'){
		return(x+y);
	}else if(c=='-'){
		return(y-x);
	}else if(c=='*'){
		return(x*y);
	}else if(c=='/'){
		return(y/x);
	}else if(c=='^'){
		return((int)pow(y, x));
	}
}
// evales postfix expression
void postfixEval(string exp){
	stack<int> s;
	for(int i=0;i<exp.length();i++){
		if(exp[i]>='1' and exp[i]<='9'){
			int x=(int)exp[i]-48;
			s.push(x);

		}else if(exp[i]=='+' or exp[i]=='-' or exp[i]=='*' or exp[i]=='/' or exp[i]=='^'){
			if(s.size()>=2){
				int x=s.top();
				s.pop();
				int y=s.top();
				s.pop();
				int z=process(x, y, exp[i]);
				s.push(z);
			}
		}

		cout << s.top() << endl;
	}
	cout << "final result: " << s.top() << endl;
}
int main(){

	string exp="1+2*3+(4*3+3*8/4)-3+6/3";
	string s=postfix(exp);
	cout << s << endl;
	postfixEval(s);
	return 0;
}