C++ Programming Code Examples C++ > Data Structures Code Examples C++ Program to Evaluate an Expression using Stacks C++ Program to Evaluate an Expression using Stacks This C++ program, using a stack data strucure, computes value of postfix expression which pushes operands and pops these values on encountering an operator. #include <iostream> #include <conio.h> #include <string.h> using namespace std; struct node { int data; node *next; }*p = NULL, *top = NULL, *save = NULL, *ptr; void push(int x) { p = new node; p->data = x; p->next = NULL; if (top == NULL) { top = p; } else { save = top; top = p; p->next = save; } } char pop() { if (top == NULL) { cout<<"underflow!!"; } else { ptr = top; top = top->next; return(ptr->data); delete ptr; } } int main() { char x[30]; int a, b; cout<<"enter the balanced expression\n"; cin>>x; for (int i = 0; i < strlen(x); i++) { if (x[i] >= 48 && x[i] <= 57) push(x[i]-'0'); else if (x[i] >= 42 && x[i] <= 47) { a=pop(); b=pop(); switch(x[i]) { case '+': push(a+b); break; case '-': push(a-b); break; case '*': push(a*b); break; case '/': push(a/b); break; } } } cout<<"ans is "<<pop()<<endl; getch(); }
