Infix To Postfix Using Stack In Java Code Example

Example: Infix to postfix converstion using stack

/*   Infix to postfix conversion in C++    Input Postfix expression must be in a desired format.    Operands and operator, both must be single character.   Only '+'  ,  '-'  , '*', '/' and '$' (for exponentiation)  operators are expected.  */ #include<iostream> #include<stack> #include<string>  using namespace std;  // Function to convert Infix expression to postfix  string InfixToPostfix(string expression);  // Function to verify whether an operator has higher precedence over other int HasHigherPrecedence(char operator1, char operator2);  // Function to verify whether a character is operator symbol or not.  bool IsOperator(char C);  // Function to verify whether a character is alphanumeric chanaracter (letter or numeric digit) or not.  bool IsOperand(char C);  int main()  { 	string expression;  	cout<<"Enter Infix Expression \n"; 	getline(cin,expression); 	string postfix = InfixToPostfix(expression); 	cout<<"Output = "<<postfix<<"\n"; }  // Function to evaluate Postfix expression and return output string InfixToPostfix(string expression) { 	// Declaring a Stack from Standard template library in C++.  	stack<char> S; 	string postfix = ""; // Initialize postfix as empty string. 	for(int i = 0;i< expression.length();i++) {  		// Scanning each character from left.  		// If character is a delimitter, move on.  		if(expression[i] == ' ' || expression[i] == ',') continue;   		// If character is operator, pop two elements from stack, perform operation and push the result back.  		else if(IsOperator(expression[i]))  		{ 			while(!S.empty() && S.top() != '(' && HasHigherPrecedence(S.top(),expression[i])) 			{ 				postfix+= S.top(); 				S.pop(); 			} 			S.push(expression[i]); 		} 		// Else if character is an operand 		else if(IsOperand(expression[i])) 		{ 			postfix +=expression[i]; 		}  		else if (expression[i] == '(')  		{ 			S.push(expression[i]); 		}  		else if(expression[i] == ')')  		{ 			while(!S.empty() && S.top() !=  '(') { 				postfix += S.top(); 				S.pop(); 			} 			S.pop(); 		} 	}  	while(!S.empty()) { 		postfix += S.top(); 		S.pop(); 	}  	return postfix; }  // Function to verify whether a character is english letter or numeric digit.  // We are assuming in this solution that operand will be a single character bool IsOperand(char C)  { 	if(C >= '0' && C <= '9') return true; 	if(C >= 'a' && C <= 'z') return true; 	if(C >= 'A' && C <= 'Z') return true; 	return false; }  // Function to verify whether a character is operator symbol or not.  bool IsOperator(char C) { 	if(C == '+' || C == '-' || C == '*' || C == '/' || C== '$') 		return true;  	return false; }  // Function to verify whether an operator is right associative or not.  int IsRightAssociative(char op) { 	if(op == '$') return true; 	return false; }  // Function to get weight of an operator. An operator with higher weight will have higher precedence.  int GetOperatorWeight(char op) { 	int weight = -1;  	switch(op) 	{ 	case '+': 	case '-': 		weight = 1; 	case '*': 	case '/': 		weight = 2; 	case '$': 		weight = 3; 	} 	return weight; }  // Function to perform an operation and return output.  int HasHigherPrecedence(char op1, char op2) { 	int op1Weight = GetOperatorWeight(op1); 	int op2Weight = GetOperatorWeight(op2);  	// If operators have equal precedence, return true if they are left associative.  	// return false, if right associative.  	// if operator is left-associative, left one should be given priority.  	if(op1Weight == op2Weight) 	{ 		if(IsRightAssociative(op1)) return false; 		else return true; 	} 	return op1Weight > op2Weight ?  true: false; }