This question already has answers here:
Convert from an infix expression to postfix (C++) using Stacks
(6 answers)
Closed 9 years ago.
Hello Stack I'm curently atempting to write a RPN converter and I'm new to C++. But I'm running into problems. Hopefully I can explain the problems in detail. Im using an array for stacking my operators. Lets use the example "5 + 8" When I get down to:
else if(infix[i] == '+' or infix[i] == '-' or infix[i] == '*' or infix[i] == '/' or infix[i] == '^'){
while(isp(stack1.top()) >= icp(infix[i])){
postfix += stack1.pop();
}
if(isp(stack1.top()) < icp(infix[i])){
stack1.push(infix[i]);
}
For some reason it will push the operator onto the stack but then it wont add the operator to the postfix string variable that im adding my elements too. the out put woul be like "5 8" I looked at my pop function and that seems to be correct but im stumped. if you can lead me in the right direction that would be great.
This is my full code:
#include <iostream>
#include <string>
#define DEFAULT_SIZE 100
using namespace std;
class Stack{
private:
char *array;
int tos, capacity;
public:
//constructors
Stack();
//Destructor
~Stack();
//Methods
void push(char a);
char pop();
char top();
int get_size();
bool is_empty();
bool is_full();
void display();
};
Stack::Stack(){
array = new char[DEFAULT_SIZE];
tos = 0;
capacity = DEFAULT_SIZE;
}
Stack::~Stack(){
delete[] array;
}
void Stack::push(char a){
if(!is_full())
array[tos++] = a;
}
char Stack::pop(){
return array[--tos];
}
char Stack::top(){
return array[tos];
}
int Stack::get_size(){
return tos;
}
bool Stack::is_empty(){
if(tos == 0)
return true;
else
return false;
}
bool Stack::is_full(){
if(tos == capacity)
return true;
else
return false;
}
void Stack::display(){
if (tos == 0)
cout<<"The stack is empty"<<endl;
else{
for (int i=0; i<tos;i++)
cout<<array[i]<<" ";
cout<<endl;
}
}
int isp(char a){
if(a == '^'){
return 3;
}
else if (a == '*' or a == '/'){
return 2;
}
else if(a == '+' or a == '-'){
return 1;
}
else if(a == '('){
return 0;
}
else
return -1;
}
int icp(char a){
if(a == '^'){
return 4;
}
else if (a == '*' or a == '/'){
return 2;
}
else if(a == '+' or a == '-'){
return 1;
}
else if(a == '('){
return 4;
}
}
int main(){
string infix, postfix;
Stack stack1;
cout << "This is a Infix to Postfix Expression converter." << endl;
cout << "Enter your Infix Expression: ";
cin >> infix;
stack1.push('#');
for(int i=0;i<infix.length();i++){
if(isdigit(infix[i]) or isalpha(infix[i])){
postfix += infix[i];
}
else if(infix[i] == '+' or infix[i] == '-' or infix[i] == '*' or infix[i] == '/' or infix[i] == '^'){
while(isp(stack1.top()) >= icp(infix[i])){
postfix += stack1.pop();
}
if(isp(stack1.top()) < icp(infix[i])){
stack1.push(infix[i]);
}
}
}
cout << postfix;
return 0;
}
Also if you know anygood resource sites on C++ RPN converter feel free to share because it would be a very big help! Im going off a random algo. that I found on google.
With your example, you're just pushing the "+" sign on the stack, but you never pop it because after processing the symbol "8", you've left the for loop. I think you need another while loop to empty your stack at the end.
for(int i=0;i<infix.length();i++){
if(isdigit(infix[i]) or isalpha(infix[i])){
postfix += infix[i];
}
else if(infix[i] == '+' or infix[i] == '-' or infix[i] == '*' or infix[i] == '/' or infix[i] == '^'){
while(isp(stack1.top()) >= icp(infix[i])){
postfix += stack1.pop();
}
if(isp(stack1.top()) < icp(infix[i])){
stack1.push(infix[i]);
}
}
}
// Fetch the remaining operators from the stack
while(!stack1.is_empty()){
postfix += stack1.pop();
}
cout << postfix;
Beware of bugs, as I couldn't test this code myself.
Related
Been scratching my head for hours already and I have no clue what my mistake is. I'm following my professor's derived algorithm step by step and I don't know why it isn't working properly.
Here's the derived Algorithm:
Here's the code that I tried to make:
#include <iostream>
#include "ecpe202.h"
#define Max 100
using namespace std;
int getICP(char x){
if (x == ')'){
return 0;
}
else if (x == '^'){
return 4;
}
else if (x == '*' || x == '/'){
return 2;
}
else if (x == '+' || x == '-'){
return 1;
}
else if (x == '('){
return 4;
}
}
int getISP(char x){
if (x == ')'){
return 0;
}
else if (x == '^'){
return 3;
}
else if (x == '*' || x == '/'){
return 2;
}
else if (x == '+' || x == '-'){
return 1;
}
else if (x == '('){
return 0;
}
}
bool isOperator(char ch){
if (ch == '+' || ch == '-' || ch == '*' || ch == '/' || ch == '^' || ch == '*' || ch == '(' || ch == ')'){
return (true);
}
else{
return (false);
}
}
int main(){
char infix[Max];
char ch;
int length;
myQueue que;
myStack stk;
createQ(que);
createS(stk);
cout << "Enter an infix Expression: ";
cin >> infix;
cout << endl << endl;
cout << "The postfix Expression: ";
length = strlen(infix);
for (int i = 0; i < length; i++){
addQ(que, infix[i]);
}
while (!isEmptyQ(que)){
ch = retrieveQ(que);
//start of infix to postfix algo
//1. push
if (ch == '('){
pushS(stk, ch);
}
//2. if scanned is operand
if (!isOperator(ch)){
cout << ch;
}
else{
//2.1 push if...
if (isEmptyS(stk) || getICP(ch) > getISP(topS(stk)) || topS(stk) == '('){
pushS(stk, ch);
}
//2.2. pop all operators
else{
while(!isEmptyS(stk) && getISP(topS(stk)) >= getICP(ch) || topS(stk) == '('){
cout << popS(stk);
}
}
pushS(stk, ch);
}
//3. If scanned ')'
bool loop = true;
if (ch == ')'){
do{
if (ch == '('){
loop = false;
}
else{
cout << popS(stk);
}
}while(loop == true);
}
//repeat 1-3
}
cout << endl;
}
For the ecpe202.h:
#include<dos.h>
#include<windows.h>
#define FOREVER true
#define MAXSTACK 100
#define MAXQUEUE 100
using namespace std;
struct myStack{
int tos;
char s[MAXSTACK];
};
struct myQueue{
int head, tail, q[MAXQUEUE];
};
//STACK
void createS(myStack &S){
S.tos=-1;
}
void pushS(myStack &S, char item){
S.s[++S.tos] = item;
}
char popS(myStack &S){
return(S.s[S.tos--]);
}
char topS(myStack S){
return (S.s[S.tos]);
}
bool isFullS(myStack S){
if(S.tos == MAXSTACK - 1)
return true;
return false;
}
bool isEmptyS(myStack S){
if (S.tos == -1)
return true;
return false;
}
//QUEUE
void createQ(myQueue &Q){
Q.head = 0;
Q.tail = 0;
}
void addQ(myQueue &Q, char item){
Q.q[Q.tail++] = item;
Q.tail %= MAXQUEUE;
}
char retrieveQ(myQueue &Q){
char temp;
temp = Q.q[Q.head++];
Q.head %= MAXQUEUE;
return temp;
}
bool isFullQ(myQueue Q){
if (Q.tail == MAXQUEUE)
return true;
return false;
}
bool isEmptyQ(myQueue Q){
if (Q.tail == Q.head)
return true;
return false;
}
//GOTOXY
void gotoxy(int x, int y){
COORD coord;
coord.X = x;
coord.Y = y;
SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), coord);
}
void clrscr(){
system("CLS");
}
The output that my code:
What seems to be wrong in my program? tried re-reading it a couple of times and I still can't fix it.
I have implemented Shunting yard algorithm using stack in c++.
Well it is working quite well on inputs from SPOJ example inputs but when I input:
1
(((a+b) * (c+r)^(t+b)-n)^(c-(d * e))-b)+(c+(e-(d^r)))
I get a runtime error.
Note: I only get a runtime error when I call infixToPostfix() and use the above input and not when I comment it out.
Submission to SPOJ and running on ideone(with input above) results in a runtime error.
I really can't understand this behaviour of my program, so any help is welcomed.
I have tried some random inputs and it seems to work fine on them.
Even though they had spaces around operators.
#include<iostream>
#include<vector>
#include<math.h>
#include<stack>
#include<strings.h>
using namespace std;
void infixToPostfix(string st);
int pr(char s);
int main() {
int t;
scanf("%d",&t);
cin.ignore();
string st; // input string
while(t--)
{
getline(cin,st);
cin.sync();
cout<<st<<endl;
infixToPostfix(st);
}
return 0;
}
int pr(char s) // to check precedence
{
if(s == '^')
{
return 4;
}
else if(s == '*')
{
return 3;
}
else if(s == '/')
{
return 3;
}
else if(s == '+')
{
return 2;
}
else if(s == '-')
{
return 2;
}
else {
return 0;
}
}
void infixToPostfix(string st)
{
stack<char>op; //stack to hold operators and bracket
st += 'n';
int l = st.size();
op.push('0');
string fst; //final string
for(int x = 0;x<l;x++)
{
if(st[x] == '(')
{
op.push(st[x]);
}
else if(st[x] == ')')
{
while(op.top() != '(' && !op.empty())
{
fst +=op.top();
op.pop();
}
op.pop();
}
else if(st[x] == '+' || st[x] == '-' || st[x] == '*' ||st[x] == '/' ||st[x] == '^')
{
if(pr(st[x]) <= pr(op.top()))
{
fst += op.top();
op.pop();
op.push(st[x]);
}
else{
op.push(st[x]);
}
}
else if(st[x] == 'n'){
while(op.size() != 0)
{
if(op.top() != '0')
{fst += op.top();}
op.pop();
}
}
else if((st[x] >= 'a' || st[x] <= 'z' )&& st[x] != ' ')
{
fst += st[x];
}
}
printf("%s\n",fst.c_str());
}
I've got a few different functions that on their own work fine. Now I am trying to put them together into one file. My debugger is throwing segmentation faults in the infixToPostfix function.
When I watch the ns variable, it does not show anything getting assigned to it, but it prints out the postfix expression when I actually run the code. When ns passes into PostfixEvaulation, it runs to the top member function of TemplateStack and crashes with:
terminate called after throwing an instance of "std::string"
This only happens when I pass a string with an operator. When I pass a string of just numbers, everything runs fine,
but it still does not seem to call PostfixEvaluation.
#include <iostream>
#include <sstream>
#include <string>
#include <typeinfo>
using namespace std;
//Class Template Stack declaration
template <class T>
class TemplateStack {
public:
typedef T type;
TemplateStack()
{
max_size_ = 50;
TopOfStack = 0;
data_ = new T[max_size_];
} //Default Constructor taking no parameters
void push(T element)
{
if (TopOfStack == max_size_)
throw string("Stack's underlying storage is overflow");
TopOfStack++;
data_[TopOfStack] = element;
}
void pop() {
if (TopOfStack == -1)
throw string("Stack is empty");
TopOfStack--;
}
T top() {
if (TopOfStack == -1)
throw string("Stack is empty");
return data_[TopOfStack];
}
private:
int TopOfStack; //Generic data type for the top element of stack
size_t max_size_;
T* data_;
};
//Function to Evauluate the Postfix notation expresion
int PostfixEvaulation(string input){
//string input;
int operand1, operand2, result,number;
TemplateStack<char>operation;
stringstream temp;
int i=0;
while (i < input.length())
{
if (isdigit(input[i]))
{
operation.push(input[i]);
}
else
{
operand2 = operation.top();
temp << operation.top();
operation.pop();
operand1 = operation.top();
temp << operation.top();
operation.pop();
switch(operand1,operand2)
{
case '+': result=operand1 + operand2;
break;
case '-': result=operand1 - operand2;
break;
case '*': result=operand1 * operand2;
break;
case '/': result=operand1 / operand2;
break;
}
operation.push(result);
}
i++;
}
cout << "The result is: "<<temp.str()<<endl;
//cin.ignore(numeric_limits<streamsize>::max(), '\n');
return 0;
}
//Function to return precedence of operators
int prec(char c)
{
if(c == '^')
return 3;
else if(c == '*' || c == '/')
return 2;
else if(c == '+' || c == '-')
return 1;
else
return -1;
}
//Function: Convert Infix to Postfix
void infixToPostfix(string s)
{
TemplateStack<char> st;
st.push('N');
int l = s.length();
string ns;
for (int i = 0; i < l; i++) {
// If the scanned character is an operand, add it to output string.
if ((s[i] >= 'a' && s[i] <= 'z') || (s[i] >= 'A' && s[i] <= 'Z')) {
ns += s[i];
}
// If the scanned character is an ‘(‘, push it to the stack.
else if (s[i] == '(') {
st.push('(');
}
// If the scanned character is an ‘)’, pop and to output string from the stack
// until an ‘(‘ is encountered.
else if (s[i] == ')') {
while (st.top() != 'N' && st.top() != '(') {
char c = st.top();
st.pop();
ns += c;
}
if (st.top() == '(') {
char c = st.top();
st.pop();
}
}
//If an operator is scanned
else {
while (st.top() != 'N' && prec(s[i]) <= prec(st.top())) {
char c = st.top();
st.pop();
ns += c;
}
st.push(s[i]);
}
}
//Pop all the remaining elements from the stack
while (st.top() != 'N') {
char c = st.top();
st.pop();
ns += c;
}
cout << "Here is the ns variable: "<< ns << endl;
PostfixEvaulation(ns);//Call the PostFixEvaluationFunction with the ns (postfix notation) variab
}
//Function: User inputs Expression
void GetInput(){
string input;
cout << "Enter Infix Expression: ";
getline(cin, input);
infixToPostfix(input);
}
int main()
{
GetInput();
}
I am a beginner using the stack so I been trying to do different exercises on it. I'm trying to convert infix->postfix. The xcode debugger says "Use of class template 'stack'requires template arguments'. Here is my code.
#include<iostream>
#include<stack>
#include<string>
using namespace std;
bool IsOperand(char ch)
{
if ((ch >= '0' && ch <= '9') || (ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z')) {
return true;
}
return false;
}
bool IsOperator(char C)
{
if (C == '+' || C == '-' || C == '*' || C == '/' || C == '^') {
return true;
}
return false;
}
bool IsLeftParenthesis(char ch)
{
if (ch == '(') {
return true;
}
return false;
}
bool IsRightParenthesis(char ch)
{
if (ch == ')') {
return true;
}
return false;
}
bool Flag(char ch)
{
if (!IsOperand(ch) || !IsOperator(ch) || !IsLeftParenthesis(ch) || !IsRightParenthesis(ch)) {
return false;
}
return true;
}
int IsRightAssociative(char op)
{
if (op == '^') {
return true;
}
return false;
}
int GetOperatorWeight(char op)
{
int weight = -1;
switch (op) {
case '+':
case '-':
weight = 1;
break;
case '*':
case '/':
weight = 2;
break;
case '^':
weight = 3;
break;
}
return weight;
}
bool 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.
// BUT REMEMBER...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;
}
string InfixToPostfix(string expression)
{
stack S;
string postfix = "";
for (auto& elem : expression) {
if (Flag(elem)) {
continue;
}
// If character is operator, pop two elements from stack, perform operation and push the result back.
else if (IsOperator(elem)) {
while (!S.empty() && S.top() != '(' && HasHigherPrecedence(S.top(), elem)) {
postfix += S.top();
S.pop();
}
S.push(elem);
}
else if (IsOperand(elem)) {
postfix += elem;
}
else if (elem == '(') {
S.push(elem);
}
else if (elem == ')') {
while (!S.empty() && S.top() != '(') {
postfix += S.top();
S.pop();
}
S.pop();
}
}
while (!S.empty()) {
postfix += S.top();
S.pop();
}
return postfix;
}
int main()
{
// std::string expression = "54/(5^2)+(6^2^3)";
std::string expression = "A+(BC-(D/E^F)G)H";
std::string postfix = InfixToPostfix(expression);
std::cout << "Output = " << postfix << "\n";
}
Here specificially where the error is happening.
string InfixToPostfix(string expression)
{
stack S;
It says
Stack S -> Use of class template 'stack'requires template arguments'
Stack is a container, you need to specify the type of the container like:
stack <int> S;
or in you case it is stack of char:
stack <char> S;
I'm pretty green at C++, and I have to make an infix to postfix calculator that supports sin() and cos(), and it has to be a 2 variable function, something like z=3x*sin(3+4y), I already got the parser from infix to postfix, but I don't know how to implement sin and cos, I've been told that I could set them as operator, like +, -, /, etc. and to set a specific token for them, like "s" for sin() and "c" for cos() but I don't exactly know how, and I don't know either how to implement the variables x & y, I know that this is not something I should be asking, but I'm just tired and desperate.
Here's the code I have. I'm using Ubuntu 11:
#include <iostream>
#include <cmath>
#include <cstdlib>
#include <string>
#define MAX_SIZE 20
using namespace std;
template<class T> class Stack
{
private:
T item[MAX_SIZE];
int top;
public:
Stack()
{
top = -1;
}
void push(T data)
{
if(!this->is_full())
item[++top] = data;
else
{
cout << "Stack Error" << endl;
exit(10);
}
}
T pop()
{
if(!this->is_empty())
{
return item[top--];
}
else
{
cout << "Stack is Empty" << endl;
exit(11);
}
}
int size()
{
return top + 1;
}
bool is_empty()
{
if(top == -1)
return true;
else
return false;
}
bool is_full()
{
if(top == MAX_SIZE - 1)
return true;
else
return false;
}
void display()
{
for(int i = 0; i < this->size(); i++)
{
cout << item[i] << " ";
}
cout << endl;
}
T return_top()
{
return item[top];
}
};
class Convert
{
private:
bool num_flag;
bool two_digit_flag;
public:
Convert();
string return_with_bracket(string infix);
void to_Postfix(string infix,char postfix[]);
bool prcd(char op1, char op2);
int isOperand(char op);
int isOperator(char op);
bool return_flag()
{
return num_flag;
}
};
Convert::Convert()
{
this->num_flag = false;
this->two_digit_flag = false;
}
string Convert::return_with_bracket(string infix)
{
return("(" + infix + ")");
}
bool Convert::prcd(char op1, char op2)
{
if((op1 == '+' || op1 == '-' || op1 == '*' || op1 == '/') && op2 == '(')
return true;
if(op1=='+' && op2=='+')
return true;
if(op1=='-' && op2=='-')
return false;
if(op1=='-' && op2=='+')
return false;
if(op1=='+' && op2=='-')
return false;
if(op1=='/' && op2=='/')
return false;
if(op1=='/' && (op2=='-' || op2=='+'))
return true;
if(op1=='*' && (op2=='+' || op2=='-'))
return true;
if((op1 == '-' || op1 == '+') && (op2 =='*' || op2 == '/'))
return false;
if((op1 == '$' || op1 == '+') && (op2 =='*' || op2 == '/' || op2=='-'))
return true;
if((op1 == '-' || op1 == '+' || op1 =='*' || op1 == '/')&& op2=='^')
return false;
if(op1 == '^' && ( op2 == '+' || op2 =='*' || op2 == '/' || op2=='-'))
return false;
}
int Convert::isOperand(char op)
{
return(op >= '0' && op <= '9');
}
int Convert::isOperator(char op)
{
return(op =='+' || op =='-' || op == '/' || op =='*' || op =='^');
}
void Convert::to_Postfix(string infix, char postfix[])
{
int position, outpos=0;
char c;
int count = 0;
char temp;
char stacktop;
Stack<char> stack;
for(position = 0; (c = infix[position]) != '\0'; position++)
{
if(this->isOperand(c))
{
postfix[outpos++] = c;
this->num_flag = true;
count++;
if(count >= 2)
{
this->two_digit_flag = true;
}
}
else if(this->isOperator(c))
{
count = 0;
if(isOperator(infix[position]) && isOperator(infix[position + 1]))
{
cout << " '\' aMissing argument in between " << infix[position] << " and " << infix[position + 1] << " in column " << position + 1 << endl;
exit(9);
}
if(this->prcd(c, stacktop))
{
stacktop = stack.return_top();
stack.push(c);
stacktop = c;
}
else
{
while(true)
{
temp = stack.pop();
postfix[outpos++] = temp;
stacktop = stack.return_top();
if(prcd(c, stacktop) || stacktop == '(')
break;
}
stack.push(c);
stacktop = stack.return_top();
}
}
else if(c == '(')
{
count = 0;
stack.push(c);
stacktop = stack.return_top();
}
else if(c == ')')
{
count = 0;
while(1)
{
if(stack.size() == 0)
{
cout << "Warning!! Number of ')' is greater than '('" << endl;
exit(2);
}
temp = stack.pop();
if(temp != '(')
{
postfix[outpos++] = temp;
}
else
{
break;
}
}
stacktop = stack.return_top();
}
else
{
cout << "Invalid input";
exit(3);
}
if(infix[position] == ')' && infix[position + 1] == '(')
{
stack.push('*');
stacktop = stack.return_top();
}
}
if(stack.size() != 0)
{
cout << "Warning!!Number of '(' is greater than ')'" << endl;
// exit(6);
}
if(!this->return_flag())
{
cout << "You must Enter Numeric value for calculation" << endl;
cout << "This program cannot perform operations on variables";
exit(5);
}
if(this->two_digit_flag)
{
cout << "Sory! Althoug u may have entered right string" << endl;
cout << "this program is only for single digit operation" << endl;
exit(8);
}
postfix[outpos] = '\0';
}
class Evaluate
{
public:
double eval(char expr[], Convert &);
double oper(int symb, double op1, double op2);
};
double Evaluate::oper(int symb, double op1, double op2)
{
switch(symb)
{
case '+': return (op1 + op2);
case '-': return (op1 - op2);
case '*': return (op1 * op2);
case '/': return (op1 / op2);
case '^': return (pow(op1, op2));
}
}
double Evaluate::eval(char expr[], Convert &convert)
{
int c, position;
char temp1;
int count = 0;
double opnd1, opnd2, value;
Stack<double> stack;
for(position = 0; (c = expr[position]) != '\0'; position++)
{
if(convert.isOperand(c))
{
temp1 = double(c - '0');
stack.push(temp1);
}
else
{
opnd2 = stack.pop();
if(stack.size() == 0)
{
cout << "This program cannot process unary operation";
exit(1);
}
opnd1 = stack.pop();
value = oper(c, opnd1, opnd2);
stack.push(value);
}
}
if(stack.size() >= 2)
{
cout << "Sory! this program cannot calculate this" << endl;
cout << "Enter +, *, /, - or ^ between bracket" << endl;
exit(4);
}
return (stack.pop());
}
int main()
{
Convert convert;
Evaluate evaluate;
string bracketted_infix;
char infix[50], postfix[50];
char choice;
while(1)
{
cout << "Enter string: ";
cin >> infix;
cout << endl;
cout << "Entered String: " << infix << endl;
bracketted_infix = convert.return_with_bracket(infix);
convert.to_Postfix(bracketted_infix, postfix);
cout << "Equivalent Postfix string: " << postfix << endl;
cout << "RESULT: ";
cout << evaluate.eval(postfix, convert);
cout << "\nCalculate another string?(y/n) ";
cin >> choice;
cout << endl;
if(choice == 'n')
break;
}
return 0;
}