After-the-fact Notes on Homework 1

Notes:

• Strictly speaking, you don't have to declare that main() returns an int, but good programming practice dictates that you should do so anyway.
• Exercise 1.26 raises some interesting questions about how to write code that is both clear and efficient. For example, it is both more clear and more effic ent to write this:
  
  cout << "The product is " << num_1 * num_2 * num_3 << endl;
  
  than this:
  
  int product;
  product = num_1 * num_2 * num_3;
  cout << "The product is " << product << end;
  
  because the first way uses fewer lines of code (easier to understand) and saves the memory needed for one variable (more efficient). But what about the sum and average? It may seem surprising, but it is just as efficient to use:
  
  cout << "The sum is " << num_1 + num_2 + num_3 << endl;
  cout << "The average is " << (num_1 + num_2 + num_3) / 3 << en d;
  
  as it would be introduce a variable named sum that gets the sum of the three numbers, and then to do something like this:
  
  cout << "The sum is " << sum << endl;
cout << "The average is " << sum / 3 << endl;

The reason is that almost any compiler will recognize that the sum of the three numbers is needed twice and will generate the code to calculate the sum just once and preserve the value to use in the second statement automatically. Thus, avoiding the variable sum gives your reader less code to read while still making the meaning of the program clear, and it produces an equally efficient program.

  Computing the minimum and maximum values can be done in a number of ways. This is probably the simplest one, because it avoids the need for extra variables:
  
  

  cout << "The smallest is ";
  if ((num_1 < num_2) && (num_1 < num_3))
    cout << num_1 << endl;
  if ((num_2 < num_1) && (num_2 < num_3))
    cout << num_2 << endl;
  if ((num_3 < num_1) && (num_3 < num_2))
    cout << num_3 << endl;
  

  Unfortunately, you wouldn't know about "&&" when you finished reading Chapter 1, so you might use auxiliary variables for the minimum and maximum, like this:

  int minimum = num_1;
    if (num_2 < minimum) minimum = num_2;
    if (num_3 < minimum) minimum = num_3;
    cout << "Minimum is " << minimum << endl;
  

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