Application: Summing the Even Integers from 2 to 20

The program of Fig. 5.5 uses a for statement to sum the even integers from 2 to 20. Each iteration of the loop (lines 11–12) adds control variable number’s value to variable total.

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 1   // Fig. 5.5: fig05_05.cpp
 2   // Summing integers with the for statement.
 3   #include <iostream>
 4   using namespace std;
 5
 6   int main()
 7   {
 8      unsigned int total = 0; // initialize total
 9
10      // total even integers from 2 through 20
11      for ( unsigned int number = 2; number <= 20; number += 2 )
12         total += number;                                       
13
14      cout << "Sum is " << total << endl; // display results
15   } // end main

Sum is 110

Fig. 5.5. Summing integers with the for statement.

The body of the for statement in Fig. 5.5 actually could be merged into the increment portion of the for header by using the comma operator as follows:

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for ( unsigned int number = 2; // initialization
      number <= 20; // loop continuation condition
      total += number, number += 2 ) // total and increment
   ; // empty body

Image Good Programming Practice 5.1

Although statements preceding a for and statements in the body of a for often can be merged into the for header, doing so can make the program more difficult to read, maintain, modify and debug.

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