6.8 The Assignment Anywhere Side Effect

I l @ ve RuBoard

C++ allows the use of assignment statements almost anyplace. For example, you can put an assignment statement inside another assignment statement:

 // don't program like this average = total_value / (number_of_entries = last - first); 

This is the equivalent of saying:

 // program like this number_of_entries = last - first;  average = total_value / number_of_entries; 

The first version buries the assignment of number_of_entries inside the expression. Programs should be clear and simple and should not hide anything. The most important rule of programming is KEEP IT SIMPLE.

C++ also allows you to put assignment statements in the while conditional. For example:

 // do not program like this while ((current_number = last_number + old_number) < 100)      std::cout << "Term " << current_number << '\n'; 

Avoid this type of programming. Notice how much clearer the logic is in the following version:

 // program like this while (true) {      current_number = last_number + old_number;      if (current_number >= 100)           break;      std::cout << "Term " << current_number << '\n';  } 

Question 6-1: For some strange reason, the program in Example 6-4 thinks that everyone owes a balance of 0 dollars. Why?

Example 6-4. balance/balance.cpp

 #include <iostream> int   balance_owed;     // amount owed  int main(  ) {     std::cout << "Enter number of dollars owed:";     std::cin >> balance_owed;     if (balance_owed = 0)         std::cout << "You owe nothing.\n";     else         std::cout << "You owe " << balance_owed << " dollars.\n";     return (0); } 

Sample output:

 Enter number of dollars owed:  12  You owe 0 dollars. 

I l @ ve RuBoard