6.8 The Assignment Anywhere Side Effect

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.