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50

answers:

1

i am trying to write program for evaluate Postfix-expression
code:

#include <iostream>
#include <cstring>
#include <stack>
#include <ostream>
using namespace std;
int main(int argc,char *argv[]){

    char *a=argv[1];
    int n=strlen(a);
    stack<int>s;
    for (int i=0;i<n;i++)
    {
         if (a[i]=='+')
     s.push(s.pop()+s.pop());
      if (a[i]=='*')
              s.push(s.pop() * s.pop());

           if ((a[i]>='0') && (a[i]<='9'))
               s.push(0);
           while ((a[i]>='0') && (a[i]<='9'))
               s.push(10*s.pop()+(a[i++]-'0'));
    }


    cout<<s.pop()<<endl;

     return 0;
} 

but errors says that

1>c:\users\david\documents\visual studio 2010\projects\compilers\compilers.cpp(16): error C2296: '*' : illegal, left operand has type 'void'
1>c:\users\david\documents\visual studio 2010\projects\compilers\compilers.cpp(16): error C2297: '*' : illegal, right operand has type 'void'
1>c:\users\david\documents\visual studio 2010\projects\compilers\compilers.cpp(21): error C2297: '*' : illegal, right operand has type 'void'
1>c:\users\david\documents\visual studio 2010\projects\compilers\compilers.cpp(25): error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'void' (or there is no acceptable conversion)

i thought that i have to stack of string type or char type but no one works and please help

+1  A: 

The pop function justs pops but does not return anything.

You should use the top to get the top value and then call pop

So

s.push(s.pop() * s.pop());

should be changed to:

int temp1 = s.top();
s.pop();
int temp2 = s.top();
s.pop();
s.push(temp1 * temp2);
codaddict