2d barcode generator vb.net Section 3.10 on page 46.) EXAMPLE 3.13 Using Nested Selection Statements in Software

Generator EAN-13 in Software Section 3.10 on page 46.) EXAMPLE 3.13 Using Nested Selection Statements

This program has the same effect as those in Example 3.5 on page 39 and Example 3.8 on page 41. This version uses nested if..else statements to find the minimum of three integers: int main() { int n1, n2, n3; cout << "Enter three integers: "; cin >> n1 >> n2 >> n3; if (n1 < n2) if (n1 < n3) cout << "Their minimum is " << n1 << endl; else cout << "Their minimum is " << n3 << endl; else // n1 >= n2 if (n2 < n3) cout << "Their minimum is " << n2 << endl;

CHAP. 3]

else cout << "Their minimum is " << n3 << endl; } Enter three integers: 77 33 55 Their minimum is 33

In this run, the first condition (n1 < n2) is false, and the third condition (n2 < n3) is true, so it reports that n2 is the minimum.

This program is more efficient than the one in Example 3.8 on page 41 because on any run it will evaluate only two simple conditions instead of three compound conditions. Nevertheless, it should be considered inferior because its logic is more complicated. In the trade-off between efficiency and simplicity, it is usually best to choose simplicity. EXAMPLE 3.14 A Guessing Game

This program finds a number that the user selects from 1 to 8: int main() { cout << "Pick a number from 1 to 8." << endl; char answer; cout << "Is it less than 5 (y|n): "; cin >> answer; if (answer == 'y') // 1 <= n <= 4 { cout << "Is it less than 3 (y|n): "; cin >> answer; if (answer == 'y') // 1 <= n <= 2 { cout << "Is it less than 2 (y|n): "; cin >> answer; if (answer == 'y') cout << "Your number is 1." << endl; else cout << "Your number is 2." << endl; } else // 3 <= n <= 4 { cout << "Is it less than 4 (y|n): "; cin >> answer; if (answer == 'y') cout << "Your number is 3." << endl; else cout << "Your number is 4." << endl; } } else // 5 <= n <= 8 { cout << "Is it less than 7 (y|n): "; cin >> answer; if (answer == 'y') // 5 <= n <= 6 { cout << "Is it less than 6 (y|n): "; cin >> answer; if (answer == 'y') cout << "Your number is 5." << endl; else cout << "Your number is 6." << endl; } else // 7 <= n <= 8 { cout << "Is it less than 8 (y|n): "; cin >> answer; if (answer == 'y') cout << "Your number is 7." << endl; else cout << "Your number is 8." << endl; } } } By repeatedly subdividing the problem, it can discover any one of the 8 numbers by asking only three questions. In this run, the user s number is 6.

The algorithm used in Example 3.14 is called the binary search. It can be implemented more simply. (See Example 6.14 on page 135.) 3.10 THE else if CONSTRUCT Nested if..else statements are often used to test a sequence of parallel alternatives, where only the else clauses contain further nesting. In that case, the resulting compound statement is usually formatted by lining up the else if phrases to emphasize the parallel nature of the logic. EXAMPLE 3.15 Using the else if Construct for Parallel Alternatives

This program requests the user s language and then prints a greeting in that language: int main() { char language; cout << "Engl., Fren., Ger., Ital., or Rus. (e|f|g|i|r): "; cin >> language; if (language == 'e') cout << "Welcome to ProjectEuclid."; else if (language == 'f') cout << "Bon jour, ProjectEuclid."; else if (language == 'g') cout << "Guten tag, ProjectEuclid."; else if (language == 'i') cout << "Bon giorno, ProjectEuclid."; else if (language == 'r') cout << "Dobre utre, ProjectEuclid."; else cout << "Sorry; we don't speak your language."; } Engl., Fren., Ger., Ital., or Rus. (e|f|g|i|r): i Bon giorno, ProjectEuclid. This program uses nested if..else statements to select from the five given alternatives. As ordinary nested if..else statements, the code could also be formatted as if (language == 'e') cout << "Welcome to ProjectEuclid."; else if (language == 'f') cout << "Bon jour, ProjectEuclid."; else if (language == 'g') cout << "Guten tag, ProjectEuclid."; else if (language == 'i') cout << "Bon giorno, ProjectEuclid."; else if (language == 'r') cout << "Dobre utre, ProjectEuclid."; else cout << "Sorry; we don't speak your language."; But the given format is preferred because it displays the parallel nature of the logic more clearly. It also requires less indenting.