Write a program to evaluate a postfix expression using stacks.

#include<iostream>
#include<stack>
#include<string.h>
using namespace std;
class test
{
stack<int> s;
char exp[20];
int len,a,b,res,op=0;
public:
void getdata()
{
cout<<"Enter the Expression( e.g. 24 56 + ) : ";
gets(exp);
len=strlen(exp);
}
bool opr(char ch)
{
if(ch=='+'||ch=='-'||ch=='*'||ch=='/')
return true;
else
return false;
}
void result(int a,int b,char ch)
{
switch(ch)
{
case '+':res=a+b;
break;
case '-':res=a-b;
break;
case '*':res=a*b;
break;
case '/':res=a/b;
break;
}
}
void cal()
{
for(int i=0;i<len;i++)
{
if(exp[i]==' ')
continue;
else if(opr(exp[i]))
{
a=s.top(); s.pop();
b=s.top(); s.pop();
result(a,b,exp[i]);
s.push(res);
}
else
{
int z=int(exp[i])-'0';
op=op*10+z;
if(exp[i+1]==' ')
{
s.push(op);
op=0;
}
}
}
}
void display()
{
cout<<"\n\nResult is:"<<s.top();
}
};
int main()
{
test t;
t.getdata();
t.cal();
t.display();
cout<<"\n/*\nName-Sanjampreet Singh\nRoll Number-1507967\n*/";
}

Output:


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