1 CIS Jan-06

2 Overview Selection Statements –If Statement –Else –Nested If-Else –Switch Repetition Statements –While statement –For Statement –Infinite loops –Do-While Statement –Break –Continue Formatted Output

3 Selection Statements if-else –Decision making statement switch –Allows choice: one out of several options

4 If Statement if ( test ) statement; if ( test ) { statements; } if true (i.e. != 0) do statement if false (i.e. == 0) skip it

5 If Statement if ( x == 7 ) cout << “you win\n”; if ( value != 0) { statements; } SAME AS: if (value) { statements; } Remember to use == to compare. Using = will assign the value, and will ALWAYS be true.

6 Else if ( test ) true statement; else false statement; if ( test ) { true statements; } else { false statements; }

7 Else cout << “Please enter a positive integer”; cin >> value; if (value > 0) cout << “Thank you!\n”; else { cout << “The value entered was not positive\n”; cout << “I will use the value 10 \n”; value = 10; }

8 Nested If-Else if (x > 0) cout << "x is positive"; else if (x < 0) cout << "x is negative"; else cout << "x is 0";

9 Nested If-Else cin >> command; if ( command == ‘u’ ) cout << “Move up” << endl; else if ( command == ‘d’ ) cout << “Move down” << endl; else if ( command == ‘l’ ) cout << “Move left” << endl; else if ( command == ‘r’ ) cout << “Move right” << endl; else cout << “Invalid command received << endl;

10 Nested If-Else cin >> command; if ( command == ‘u’ ) cout << “Move up” << endl; else if ( command == ‘d’ ) cout << “Move down” << endl; else if ( command == ‘l’ ) cout << “Move left” << endl; else if ( command == ‘r’ ) cout << “Move right” << endl; else cout << “Invalid command received << endl;

11 Switch switch (value) { case constant1: statement1; statement; break; case constant2: statement2; break; default: statement; break; } Cases may be in any order “case” is terminated with a : (colon) “constants” can be integers or characters Cases may have several statements break jumps out of the construct default is optional

12 Switch cin >> choice; switch (choice) { case 0: cout << “Just a beginner huh?\n”; moves = 15; break; case 1: case 2: case 3: cout << “OK, let’s begin \n”; moves = 10; break; case 4: cout << “You only have 7 moves \n”; moves = 7; break; default: cout << “Incorrect selection \n”; moves = 0; break; } Only way to have several choices do the same thing.

13 If-else-if vs Switch cin >> command; if ( command == ‘u’ ) cout << “Move up” << endl; else if ( command == ‘d’ ) cout << “Move down” << endl; else if ( command == ‘l’ ) cout << “Move left” << endl; else if ( command == ‘r’ ) cout << “Move right” << endl; else cout << “Invalid command received << endl; cin >> command; switch ( command ) { case ‘u’: cout << Move up” << endl; break; case ‘d’: cout << “Move down” << endl; break; case ‘l’: cout << “Move left” << endl; break; case ‘r’: cout << “Move right” << endl; break; default: cout << “Invalid command received” << endl; break; }

14 Repetition Statements while loops –pretest loop for loops –pretest loop do-while loops –posttest loop pretest loop: –Test at the beginning of the loop –Condition must be set prior to loop entry. posttest loop: –Test at the end of the loop –Always executes at least once.

15 While statement while ( expression ) statement; while ( expression ) { statements; } Evaluates the expression if true (i.e. != 0) executes statement(s) While test Body true false

16 While statement while ( x < 0 ) x = x – y + z; while ( a <= b) { a = a + 1; b = b / 2; total = total + b; }

17 For Statement for ( initialize; expression; alter ) statement; for ( initialize; expression; alter ) { statement(s); } Initialize for test Body Alter false true

18 For Statement int i; for ( I = 0; I <= 10; i++) { cout << i << endl; } int answer, a, c, b; a = 0; b = 100; answer = 0; for (c = a; c <= b; c++) answer = answer + c;

19 While vs. For int i = 0; while ( i <= 10) { cout << i << endl; i++; } for (int i = 0; i <= 10; i++) cout << i << endl;

20 Beware the infinite loop! for (c = a; c <= b; 1) answer = answer + c; for ( c = a; 10; c++) answer = answer + c; while (i < 10) { cout << i << endl; } c does not change, infinite loop Always true, infinite loop i is never incremented; infinite loop

21 Do-While Statement do { body; } while ( expression ) executes statement(s) evaluates the expression if true (i.e. != 0) do body while test true false

22 Do-While statement do { cout << “Enter a number between 1 & 10 \n”; cin >> value; } while ( value 10 )

23 Break break –Can also be used to exit (jump out) of other loops as well for (i = 1; a <= b; i++) { a += i;//a = a + i b -= i;//b = b – i if (b <=0) break; c += a + b//c = c + (a + b) } Can end in two ways

24 Continue continue –Goes to the test of a loop (Does the test again) –Must be a loop not a switch while ( a < b) { cin >> a; if (a 9) continue; //process rest of loop }

25 Formatted Output #include setw( ) fixed setprecision( ) setiosflags( )

26 Formatted Output cout << 6 << endl << 18 << endl << 124 << endl << "---\n" << ( ) << endl; Results:

27 setw() Used within cout Sets field width for next output Right justifies

28 setw() //Added setw(3) to each line cout << setw(3) << 6 << endl << setw(3) << 18 << endl << setw(3) << 124 << endl << "---\n" << ( ) << endl; Results:

29 setw int a = 24; int b = 573; cout << '|' << setw(4) << a << '|' << setw(6) << b << '|' << setw(2) << b << '|' << endl; Results: | 24| 573|573|

30 fixed Used with cout Forces the display of a decimal point

31 setprecision() Used with cout Sets maximum number of decimal places –Will show less if fewer decimal values Floating point numbers only

32 setprecision() float x = ; float y = 6.4; cout << '|' << setw(7) << setprecision(2) << y << '|' << endl; cout << '|' << setw(7) << fixed << setprecision(2) << x << '|' << endl; cout << '|' << setw(7) << fixed << setprecision(2) << y << '|' << endl; Results: | 6.4| | 19.17| | 6.40|

33 setiosflags() ios::fixed ios::scientific ios::showpoint ios::showpos ios::left ios::right