6.6. Encapsulation and generalization

Encapsulation usually means taking a piece of code and wrapping it up in a function, allowing you to take advantage of all the things functions are good for. We have seen two examples of encapsulation, when we wrote printParity in Section [alternative] and isSingleDigit in Section [bool].

Generalization means taking something specific, like printing multiples of 2, and making it more general, like printing the multiples of any integer.

Here’s a function that encapsulates the loop from the previous section and generalizes it to print multiples of n.

void printMultiples (int n) {
  int i = 1;
  while (i <= 6) {
    cout << n * i << "   ";
    i = i + 1;
  }
  cout << endl;
}

To encapsulate, all I had to do was add the first line, which declares the name, parameter, and return type. To generalize, all I had to do was replace the value 2 with the parameter n.

If we call this function with the argument 2, we get the same output as before. With argument 3, the output is:

3   6   9   12   15   18

and with argument 4, the output is

4   8   12   16   20   24

By now you can probably guess how we are going to print a multiplication table: we’ll call printMultiples repeatedly with different arguments. In fact, we are going to use another loop to iterate through the rows.

int i = 1;
while (i <= 6) {
  printMultiples (i);
  i = i + 1;
}

First of all, notice how similar this loop is to the one inside printMultiples. All I did was replace the print statement with a function call.

Try running the active code below, which uses printMultiples.

The output of this program is

1   2   3   4   5   6
2   4   6   8   10   12
3   6   9   12   15   18
4   8   12   16   20   24
5   10   15   20   25   30
6   12   18   24   30   36

which is a (slightly sloppy) multiplication table. If the sloppiness bothers you, you can also use tab characters, like below.

The active code below uses tab characters to make the table neater.

Create a function called powersOfTwo which prints out a table with the powers of two up to \(2^{5}\).

Now let’s generalize the function to print out the powers of a parameter n up to \(n^{5}\). Create a function called powersOfn which takes an int n as a parameter.

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