fds10

#include<iostream>
#include<cctype>
#include<stack>
using namespace std;

// returns the value when a specific operator
// operates on two operands
int eval(int op1, int op2, char operate) {
switch (operate) {
case '': return op2 * op1;
case '/': return op2 / op1;
case '+': return op2 + op1;
case '-': return op2 - op1;
default : return 0;
}
}
int getWeight(char ch) {
switch (ch) {
case '/':
case '': return 2;
case '+':
case '-': return 1;
default : return 0;
}
}
// evaluates the postfix operation
// this module neither supports multiple digit integers
// nor looks for valid expression
// However it can be easily modified and some additional
// code can be added to overcome the above mentioned limitations
// it's a simple function which implements the basic logic to
// evaluate postfix operations using stack
int evalPostfix(char postfix[], int size) {
stack<int> s;
int i = 0;
char ch;
int val;
while (i < size) {
ch = postfix[i];
if (isdigit(ch)) {
// we saw an operand
// push the digit onto stack
s.push(ch-'0');
}
else {
// we saw an operator
// pop off the top two operands from the
// stack and evalute them using the current
// operator
int op1 = s.top();
s.pop();
int op2 = s.top();
s.pop();
val = eval(op1, op2, ch);
// push the value obtained after evaluating
// onto the stack
s.push(val);
}
i++;
}
return val;
}

// main
int main() {
char postfix[] = {'a','b','c','+','*','d','/'};
int i=0;
// cout<<"Postfix 0"<<postfix[i];
while(postfix[i]!='\0')
{
if(getWeight(postfix[i])==0)
{
cout<<" Enter value for "<<postfix[i]<<" = ";
cin>>postfix[i];
}
i++;
}
int size = sizeof(postfix);
int val = evalPostfix(postfix, size);
cout<<"\nExpression evaluates to "<<val;
cout<<endl;
return 0;
}