Operator Problem

[mkiopl]

Hey there !

Ok so i am learning from Stroustrup's book, Programming Principle and practice" ,2nd edition.
I have a problem with the / operator, to be exactly if i will write " / 8 0 ", instead of giving me " 8/0 = 0" it gives me "8/0=4"
Without any boring stuff, here is the demand (Chapter 3 Exercise 10 - from the book) :

10 Write a program that takes an operation followed by two operands and outputs the result. For
example:
+ 100 3.14
* 4 5
Read the operation into a string called operation and use an if-statement to figure out which
operation the user wants, for example, if (operation=="+"). Read the operands into variables
of type double. Implement this for operations called +, –, *, /, plus, minus, mul, and div with
their obvious meanings.

#include <iostream>
using namespace std;
int main()
{
    string operation;
    double val1,val2;
    cout<<"Please enter an operation(+,-,*,/,plus,minus,mul,div) followed by two floating-point values separated by a space: ";


        while(cin>>operation>>val1>>val2)       {

                    double res;

            if(operation == "plus" || operation=="+")  res=val1+val2;
       else if(operation == "minus"|| operation=="-")  res=val1-val2;
       else if(operation == "mul"  || operation=="*")  res=val1*val2;
       else if(operation == "div"  || operation=="/")   {

                    if(val2==0)
                        {

                        cout<<"Error! Trying to divide by zero!";

                        }

                    else{
                    res=val1/val2;}
                                                        }

        cout<<val1<<operation<<val2<<"=="<<res<<endl;
        cout<<"please try again"; }
        cout<<"exit cuz of bad input";
}

Sorry for the long post :-s

[shadowCODE]

i ran your program and did not see any unexpected output.
Everything worked fine for me.