Thursday, 9 February 2017

C++ Program For Infix to Post-fix Expression Converter

Problem :- An infix expression is the usual way we write expressions. In infix expression, operators are written in-between their operands. For example, A * ( B + C ) / D is an infix expression.
In postfix expression, operators are written after their operands. The infix expression given above is equivalent to A B C + * D /.
Good Reference Article: C++ Even or Odd Program
Logic :- This program makes use of stack. A stack is used to store elements in LIFO order. The element which comes at end is deleted first. You can imagine that MS Word uses stack to store operation in a specific order. When we perform ‘undo’ then it deletes the last operation performed.

This program takes a string of an infix expression and gives a string of post-fix operation. It simply considers the every character of the infix string and if the character being considered is a number then it is appended to the post-fix string. If it is a symbol then it is pushed in the stack. Rest of the process is quite simple. The code is also self-explanatory. 

Solution :-

#include<iostream> #include<cstring> using namespace std; class stack { private: int arr[5]; int top; int size; public: stack() { top=-1; size=5; } bool IsEmpty() { if(top==-1) { return true; } else { return false; } } bool IsFull() { if(top==size-1) { return true; } else { return false; } } void push(int data) { if(IsFull()) { cout<<"STACK IS FULL..."<<endl; } else { top++; arr[top]=data; } } int pop() { if(IsEmpty()) { cout<<"STACK IS EMPTY..."<<endl; } else { int c; c=arr[top]; top--; return c; } } void show() { if(IsEmpty()) { cout<<"STACK IS EMPTY..."<<endl; } else { for (int i=0;i<=top;i++) { cout<<"DATA ---- "<<arr[i]<<endl; } } } int getweight(char ch) { switch(ch) { case '/': case '*': return 2; case '+': case '-': return 1; default: return 0; } } void in2p(char in[],char po[],int size) { int i=0,k=0; int w; char ch; while(i<size) { ch=in[i]; w=getweight(ch); if(w==0) { po[k++]=ch; } else { if(IsEmpty()) { push(ch); } else { while(!IsEmpty() && w<=getweight(arr[top])) { po[k++]=arr[top]; pop(); } push(ch); } } i++; } while(!IsEmpty()) { po[k]=arr[top]; k++; pop(); } po[k]=0; } }; int main() { char given[]="1+2*3"; int s=strlen(given); char desired[s]; stack obj; obj.in2p(given,desired,s); cout<<"\n\n\n\t\t----------------------------------------------"; cout<<"\n\t\t| |"; cout<<"\n\t\t| INFIX TO POSTFIX EXPRESSION CONVERTER |"; cout<<"\n\t\t| |"; cout<<"\n\t\t----------------------------------------------\n"; cout<<"\t\tINFIX EXPRESSION = "<<given; cout<<"\n\n\t\tPOSTFIX EXPRESSION = "<<desired<<endl<<endl; system("pause"); };
Output :-

C++ Program For Infix to Post-fix Expression Converter

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