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// FILE: demo1.cxx
// This small demonstration shows how the throttle class is used.
#include <iostream> // Provides cout and cin
#include <cstdlib> // Provides EXIT_SUCCESS
using namespace std; // Allows all Standard Library items to be used
class throttle
{
public:
// MODIFICATION MEMBER FUNCTIONS
void shut_off( );
void shift(int amount);
// CONSTANT MEMBER FUNCTIONS
double flow( ) const;
bool is_on( ) const;
private:
int position;
};
int main( )
{
throttle sample;
int user_input;
// Set the sample throttle to a position indicated by the user.
cout << "I have a throttle with 6 positions." << endl;
cout << "Where would you like to set the throttle? " << endl;
cout << "Please type a number from 0 to 6: ";
cin >> user_input;
sample.shut_off( );
sample.shift(user_input);
// Shift the throttle down to zero, printing the flow along the way.
while (sample.is_on( ))
{
cout << "The flow is now " << sample.flow( ) << endl;
sample.shift(-1);
}
cout << "The flow is now off" << endl;
return EXIT_SUCCESS;
}
void throttle::shut_off( )
// Precondition: None.
// Postcondition: The throttle has been turned off.
{
position = 0;
}
double throttle::flow( ) const
// Precondition: shut_off has been called at least once to initialize the
// throttle.
// Postcondition: The value returned is the current flow as a proportion of
// the maximum flow.
{
return position / 6.0;
}
void throttle::shift(int amount)
// Precondition: shut_off has been called at least once to initialize the
// throttle.
// Postcondition: The throttle's position has been moved by amount (but not
// below 0 or above 6).
{
position += amount;
// Adjust the throttle if it went too high or too low
if (position < 0)
position = 0;
else if (position > 6)
position = 6;
}
bool throttle::is_on( ) const
// Precondition: shut_off has been called at least once to initialize the
// throttle.
// Postcondition: If the throttle's flow is above 0 then the function
// returns true; otherwise it returns false.
{
return (flow( ) > 0);
}
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