#include<bits/stdc++.h>
using namespace std;
int n;
string s;
vector<char> st;
vector<char> a;

void StackAndInput(){ //print stack and input vector elements
  cout<<"\n$";
  for(auto x: st)
      cout<<x;
  cout<<"\t";
  for(auto x : a)
      cout<<x;
}
void check()  //check if there any reduction possible for stack elements
{   
    for(int i=0;i<st.size();i++)
    {
        if(st[i]=='a')
        {
            st[i]='E';
            StackAndInput();
            cout<<"$\t"<<"REDUCE E->a";
            check(); // we again do checking because here we may need to reduce continousely
        }
        if(i+2<st.size() && st[i]=='E'&& (st[i+1]==('+') || st[i+1]==('*')) && st[i+2]=='E')
        {
            st.pop_back();
            st.pop_back();
            StackAndInput();
            if(st[i+1]=='+')
              cout<<"$\t"<<"REDUCE E->E+E";
            else if(st[i+1]=='*')
              cout<<"$\t"<<"REDUCE E->E*E";
        }
    }
}
int main()
{
    cout<<"GRAMMAR is : \n E->E+E \n E->E*E \n E->a\n";
    //cout<<"enter input string ";
    cin>>s;
    n=s.length();
    for(int i=0;i<n;i++)
      a.push_back(s[i]);

    cout<<"\nstack\t input\taction";
    for(int i=0;i<n;i++)
    {
        st.push_back(a[i]);
        a[i]=' '; // replace element with space so that it not visible in output
        StackAndInput();
        cout<<"$\t"<<"SHIFT->"<<st.back();
        check();
    }
    if(st.size()==1 && st[0]=='E')
        cout<<"\n\nstring accepted";
    else
        cout<<"\n\nstring rejected";
}
by

C++ Online Compiler

Write, Run & Share C++ code online using OneCompiler's C++ online compiler for free. It's one of the robust, feature-rich online compilers for C++ language, running on the latest version 17. Getting started with the OneCompiler's C++ compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as C++ and start coding!

Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}