Syntax for lab 6

Key syntax elements for lab 6

The C++ features we will add for lab 6 are structs plus arrays of structs. (Refer back to the course notes or to the previous labs for refreshers on the syntax used earlier.)

Structs and arrays of structs

Declaring a struct data type, typically in the global definitions section of our programs, after the global constant definitions but before function prototypes

// declare a data type to represent time,
//    with ints for hours and minutes,
//    and a float for seconds (0-59.9999)
struct Time {
   int hour;     // 0-23
   int minute;   // 0-59
   float second; // 0-59.9999
};

Initializing variables of a struct type

Time startTime = { 11, 30, 0.00 };  // sets hour, minute, and seconds

Accessing the fields of a struct variable using the variable.field notation

   startTime.hour = 9;
   startTime.minute = 20;
   startTime.second =  0.01;
   std::cout << "Start time is " startTime.hour << ":" << startTime.minute;
   std::cout << ":" << startTime.second);

Using a function to set the fields of a struct (i.e. pass by reference)

// sets time to 00:00:00
void setTime(Time &T);

int main()
{
   Time t;
   setTime(t);
}

void setTime(Time &T)
{
   T.hour = 0;
   T.minute = 0;
   T.second = 0;
}

Declaring and using an array of structs:

int main()
{
    const int size = 10;
    Time timevals[size]; // creating the array

    // filling it one element at a time with calls to setTime
    for (int i = 0; i < size; i++) {
        setTime(timevals[i]);
    }

    // accessing the elements directly through the array
    for (int j = 0; j < size; j++) {
        cout << "Hour: ";
        cout << timevals[j].hour; // the hour field of the j'th element
        cout << ", minute: ";
        cout << timevals[j].minute; // the minute field of the j'th element
        cout << endl;
    }
}