about constructor and switch

about constructor and switch

[learning c++]

Hi, I compiled a short code. But it does not work.
There are something wrong in constructor, substr and switch.

10.11.cpp: In member function `int Expr::eval()':
10.11.cpp:28: error: switch quantity not an integer


#include <iostream>
#include <string>

using namespace std;

class Expr{

int val1, val2, value;

string s1;

public:
Expr(const string);
int eval();
void print();
};

Expr::Expr(const string s){
string::iterator iter1;
for(iter1=s.begin();iter1!=s.end();iter1++){
if(!isdigit(*iter1))
val1=(int)s.substr(s.begin(),iter1-1);
val2=(int)s.substr(iter1+1,s.end());
s1=*iter1;
}
}
int Expr::eval(){
switch(s1){
case "+":
value=val1+val2;
return value;
break;
case "*":
value=val1*val2;
return value;
break;
case "-":
value=val1-val2;
return value;
break;
case "/":
value=val1/val2;
return value;
break;
}
}

int main(){
int output;
Expr input("5+3");
output=input.eval();
cout<<"The result is: "<<output<<endl;
return 0;
}

_________________________________________________________________
Add photos to your messages with MSN 8. Get 2 months FREE*. 
http://join.msn.com/?page=features/featuredemail

Re: about constructor and switch

[Eljay Love-Jensen]

Hi,

The switch C/C++ construct can only take an integer.

It cannot take an object (unless that object is convertible to an 
integer).  Thus, it cannot take a std::string.

It cannot take a float, double, long double.  Or a complex.  Or a pointer.

It can take a char, short, int, long or bool, or any expression which 
evaluates to such.

Some languages, such as Ada, have a more capable switch construct, which 
can handle those other situations that C/C++ cannot.

For those more complicated situations in C/C++, use a if/else if/else 
construct, or use polymorphism (where applicable).

HTH,
--Eljay