2/19/2016IT 279, Chung-Chih Li1 Branching Condition Statement list 1 T F Statement list 2 Condition Statement list T F

2/19/2016IT 279, Chung-Chih Li2 The Syntax of if and if/else statements if ( condition ) { statement list; } if ( condition ) { statement list1; } else { statement list2; } Indentation indicates that the statements in the statement list are at the level next to the if/else statement. Reserved words A Boolean expression (logical expression). In C++, 0 is false, any non-zero values will be considered as true. true false A reserved word can’t be used as an identifier

2/19/2016IT 279, Chung-Chih Li3 #include using namespace std; void main() { int a, b, c; cin >> a >> b >> c; if (a > b) { } else { } cout << “ is the biggest ” ; } if (a > c) cout << “ a: ” << a; else cout << “ c: ” << c; if (b > c) cout << “ b: ” << b; else cout << “ c: ” << c; max II

2/19/2016IT 279, Chung-Chih Li4 Operators Arithmetic operators: + - / * % Relational operators: == > = != Logical operators: || && !

2/19/2016IT 279, Chung-Chih Li5 Relational Operators cout << (1 < 0) << endl; 0 cout 0) << endl; 1 cout << (1 == 0) << endl; 0 cout << (1 <= 0) << endl; 0 cout = 0) << endl; 1 cout "0") << endl; 1 cout << ("Yes" == "yes") << endl; 0 cout "aaa") << endl; 1 cout << (2 < 3 < 4) << endl; cout 3 > 2) << endl; cout (3 > 2)) << endl; cout << (0 < 0.5 < 0.6) << endl; == > = !=

2/19/2016IT 279, Chung-Chih Li6 Logical Operators (1 || 0) ((18 <= x) && (x <= 50)) ((18 <= x) || (x <= 50)) !(x = 5) (((x % 2) == 0) && ((x % 3) == 0)) || && ! Assume x = 10 true false

2/19/2016IT 279, Chung-Chih Li7 De Morgan’s law I am not a female student.  I am not female or I am not a student. I will not be in my office or in the lab.  I will not be in my office and will not be in the lab. !(A && B) is same as !A || !B !(A || B) is same as !A && !B

2/19/2016IT 279, Chung-Chih Li8 Nested if/else statement if ( condition 1 ) { statement list; } else { statement list; } Indentation indicates the level of statements. if ( condition 2 ) { statement list; } else { statement list; }; statement list;

2/19/2016IT 279, Chung-Chih Li9 Example of nested if/else statement cout << "How many items do you want to buy? "; cin >> a; if (a == 1) discount = 0.1; else { if (a == 2) discount = 0.2; else { cout << "At most two items!!"; }

2/19/2016IT 279, Chung-Chih Li10 Enumeration data type int i,j; enum days {Mon, Tue, Wed, The, Fri, Sat, Sun}; enum days d1, d2=Wed; d1=d2; if (d1 < Sat) cout << d1 << “ It is a week day ” ; else cout << d1 << “ It is a weekend ” ;

2/19/2016IT 279, Chung-Chih Li11 Enumeration data type II enum days {Mon=1, Tue=2, Wed=3, The=4, Fri=5, Sat=6, Sun=7} d1; if (d1 < Sat) cout << d1 << “ It is a week day ” ; else cout << d1 << “ It is a weekend ” ; enum days {Mon=5, Tue=4, Wed=3, The=2, Fri=1, Sat=0, Sun=0} d1; if (d1 != 0) cout << d1 << “ It is a week day ” ; else cout << d1 << “ It is a weekend ” ;

2/19/2016IT 279, Chung-Chih Li12 Ambiguity in English I saw the girl with a telescope. I saw the girl with her boy friend.

2/19/2016IT 279, Chung-Chih Li13 bool a_member, married; // You don ’ t mean this:..... if (a_member) if (married) { cout << “ Input your spouse ’ s name: ” ; cin >> sname; } else cout << “ Sorry, can ’ t get in!! ” ; // A correct way if (a_member) { if (married) {..... } else {..... } Ambiguity in C++

2/19/2016IT 279, Chung-Chih Li14 Confusing nested if/else statement bool weekend; enum days = {Mon, Tue, Wed, The, Fri, Sat, Sun}; enum days d1=Mon, d2=Sun; d1 = Sun; if (d1 < Sat) if (d1 == Mon) cout << “ Have a nice week!!\n ” ; else cout << “ have a nice weekend\n ” ; cout << “ end\n ” ; if (d1 < Sat) { if (d1 == Mon) cout << “ Have a nice week!!\n ” ; } else cout << “ have a nice weekend\n ” ; cout << “ end\n ” ;

2/19/2016IT 279, Chung-Chih Li15 Cascaded if/else statements if (condition_1) if (condition_2) if (condition_3) if (condition_4) if (condition_5) if (condition_6) statement_1; else statement_2; if (condition_1 && condition_2 && condition_3 && condition_4 && condition_5 && condition_6) statement_1; else statement_2; = if (condition_1) { if (condition_2) if (condition_3) if (condition_4) if (condition_5) if (condition_6) statement_1; else statement_2; } =

2/19/2016IT 279, Chung-Chih Li16 Other forms of Nested if/else statements (Cascaded) I if (condition_1) statement_1; else if (condition_2) statement_2; else if (condition_3) statement_3; else if (condition_4) statement_4; else if (condition_5) statement_5; else if (condition_6) statement_6; if (condition_1) statement_1; if (condition_2) statement_2; if (condition_3) statement_3; if (condition_4) statement_4; if (condition_5) statement_5; if (condition_6) statement_6; V.S.

2/19/2016IT 279, Chung-Chih Li17 Other forms of Nested if/else statements (Cascaded) II if (condition_1) if (condition_2) if (condition_3) if (condition_4) if (condition_5) if (condition_6) statement_1; else statement_2; if (condition_1 && condition_2 && condition_3 && condition_4 && condition_5 && condition_6) statement_1; else statement_2; =

2/19/2016IT 279, Chung-Chih Li18 Switch vs. Cascaded if/else if (i == 1) statement_1; else if (i == 2) statement_2; else if (i == 3) statement_3; else if (i == 4) statement_4; else if (i == 5) statement_5; else if (i == 6) statement_6; switch (i) { case 1: statement_1; break; case 2: statement_2; break; case 3: statement_3; break; case 4: statement_4; break; case 5: statement_5; break; case 6: statement_6; break; }

2/19/2016IT 279, Chung-Chih Li19 Example of switch cout << "Input an integer as the day of the week:"; cin >> i; switch (i) { case 1 :cout << "\n Sunday"; break; case 2 : cout << "\n Monday"; break; case 3 : cout << "\n Tuesday"; break; case 4 : cout << "\n Wednesday"; break; case 5 : cout << "\n Thursday"; break; case 7 : cout << "\n Saturday"; break; case 6 : cout << "\n Friday"; break; }

2/19/2016IT 279, Chung-Chih Li20 breaks in a Switch statement if (i == 1) statement_1; else if (i == 2) { statement_2; statement_3; } else if (i == 3) statement_3; else if (i == 4) statement_4; switch (i) { case 1: statement_1; break; case 2: statement_2; case 3: statement_3; break; case 4: statement_4; }

2/19/2016IT 279, Chung-Chih Li21 LoopsBranching Condition Statement list T F Condition Statement list T F

2/19/2016IT 279, Chung-Chih Li22 while Condition Statement list T F while (Condition) { Statement list }

2/19/2016IT 279, Chung-Chih Li23 Example 1: while string ans = “ n ” ; while (ans != “ Y ” && ans != “ y ” ) { cout << “ Would you marry me? ” ; cin >> ans; } cout << “ Great!! ” ; Should I put ; here? (ans != “ Y ” || ans != “ y ” ) Can I put ; here? No!! Up to you!!

2/19/2016IT 279, Chung-Chih Li24 Example 2: while int no_times; cout << “ How many times do you want to say? ” ; cin >> no_times; while (no_times != 0) { cout << “ Hello! ” << endl; no_times--; } cout << “ End!! ” << endl; Will there be any problem? while (no_times > 0) What if one inputs –1?

2/19/2016IT 279, Chung-Chih Li25 Example 3: while int a,b,sum; cout << “ This program will return the ” ; cout << “ summation of integers from a to b.\n\n ” ; cout << “ Input two integers a and b: ” ; cin >> a >> b; while (a <= b) { sum += a; a++; } cout << “ The sum is ” << sum << endl; sum = 0; sum = sum + a; Don’t forget to set sum = 0;

2/19/2016IT 279, Chung-Chih Li26 Example 4: while int a,b,sum=0; cout << “ This program will return the sum ” ; cout << “ of odd numbers between a and b.\n\n ” ; cout << “ Input two integers a and b: ” ; cin >> a >> b; while (a <= b) { if (a % 2) sum += a; a++; } cout << “ The answer is ” << sum << endl; if (a % 2 == 0) a++; while (a <= b) { sum += a; a += 2; } 3, 4, 5, 6, 7 2, 3, 4, 5, 6, 7 a b

2/19/2016IT 279, Chung-Chih Li27 Example 5: while 3N+1 problem long n,i=0; cout << “ Input an integer: ” ; cin >> n; while (n > 1) { if (n % 2) n = 3*n+1; else n /= 2; cout << ++i << “ : ” << n << endl; } cout << “ Done!! ” << endl; W ill we always get out of a loop? That is the question!! No one knows! Input an integer:7 1:22 2:11 3:34 4:17 5:52 6:26 7:13 8:40 9:20 10:10 11:5 12:16 13:8 14:4 15:2 16:1 Done!! Press any key to continue Input an integer:11 1:34 2:17 3:52 4:26 5:13 6:40 7:20 8:10 9:5 10:16 11:8 12:4 13:2 14:1 Done!! Press any key to continue Input an integer:3759 1: :5639 3: :8459 5: : : :16 84:8 85:4 86:2 87:1 Done!! Press any key to continue

2/19/2016IT 279, Chung-Chih Li28 do-while Condition Statement list T F do { Statement list } while (Condition); string ans = “ n ” ; while (ans != “ Y ” ) { cout << “ Would you marry me? ” ; cin >> ans; } cout << “ Great!! ” ; ; is required do { cout << “ Would you marry me? ” ; cin >> ans; } while (ans != “ Y ” ); cout << “ Great!! ” ;

2/19/2016IT 279, Chung-Chih Li29 Example 1: do-while int i;.... do { cout << “ Please input a number between ” << “ 10 and 20: ” ; cin >> i; } while (i 20);......

2/19/2016IT 279, Chung-Chih Li30 Primality Test A prime number is a positive integer that cannot be factorized, i.e., no numbers other that 1 and itself can divide it. is 893 a prime? Is (893 % 2 == 0) ? Is (893 % 3 == 0) ? Is (893 % 4 == 0) ? Is (893 % 5 == 0) ? Is (893 % 6 == 0) ?. Is (893 % 892 == 0) ? We can write a loop to test these.

2/19/2016IT 279, Chung-Chih Li31 Example: Silly Primality Test long int p,r,i=2; cout << “ Input an positive integer: ” ; cin >> p; cout << p << “ is “ ; do { r = p % i; i++; } while (i < p && r != 0); if (i == p) cout << “ a prime number. ” ; else { cout << “ not a prime number. ” ; cout << “ The least factor is ” << --i; }

2/19/2016IT 279, Chung-Chih Li32 Break in a loop do { r = p % i; if (r == 0) break; i++; } while (i < p); The break statement in a loop will force the program to jump out of the loop immediately. do { cout << “ Would you marry me? ” ; cin >> ans; cout << “ Really? ” cin >> ans; } while (ans != “ Y ” && ans != “ y ” ); cout << “ Great!! ” ; if (ans == “ F ” || and == “ f ” ) break;

2/19/2016IT 279, Chung-Chih Li33 Continue in a loop The continue statement in a loop will force the program to check the loop condition immediately. do { cout << “ Would you marry me? ” ; cin >> ans; if (and != “ Y ” && ans != “ y ” ) continue; cout << “ Great? ” break; } while (true);....

2/19/2016IT 279, Chung-Chih Li34 Euclid Algorithm #include using namespace std; void main() { int a,b; cout << "Input two positive integers:"; cin >> a >> b; int r = a % b; while (r) { a = b; b = r; r = a % b; } cout << "The GCD is " << b << ".\n"; }

2/19/2016IT 279, Chung-Chih Li35 Primality Test with while loop #include using namespace std; void main() { bool is_prime=true; int d=2,p; cout << "Input a positive integers:"; cin >> p; while (d <= p/2) { if (p % d == 0) { is_prime=false; break; } d++; } if (is_prime)... } Can we change to while (d < p/2) ?

2/19/2016IT 279, Chung-Chih Li36 Primality Test with do-while loop #include using namespace std; void main() { bool is_prime=true; int d=2,p; cout << "Input a positive integers:"; cin >> p; do { if (p % d == 0) { is_prime=false; break; } d++; } while (d <= p/2); if (is_prime)... } Can we change to while (d < p/2) ?

2/19/2016IT 279, Chung-Chih Li37 Primality Test with do-while loop (a bit better) void main() { bool is_prime=true; int d=3,p; cout << "Input a positive integers:"; cin >> p; do { if ((p % d == 0) || (p % 2 == 0)) { is_prime=false; break; } d += 2; } while (d < p/2); if (is_prime)... }

2/19/2016IT 279, Chung-Chih Li38 Primality Test with do-while loop (yet another improvement) void main() { bool is_prime=true; int d=3,p; cout << "Input a positive integers:"; cin >> p; if (p % 2 == 0} is_prime=false; else do { if (p % d == 0) { is_prime=false; break; } d += 2; } while (d < p/2); if (is_prime)... } What if I forget else here?

2/19/2016IT 279, Chung-Chih Li39 Definite Loop In programming a definite loop is more welcome. is I.e., number of iterations is known before the loop begins, at least the upper bound is known. I.e., repeat the loop 100 times. Precisely speaking, there is no definite loop in C++

2/19/2016IT 279, Chung-Chih Li40 The general format for a for loop for (Initialization_action; Condition; Condition_update) { statement_list; } int n,f=1; cin >> n; for (i=2; i<=n; i++) { f *= i; } cout << “ The factorial of ” << n << “ is ” << f << “. ” ; 12 3 Factorial of n is n  (n-1)  (n-2) ...2  1

2/19/2016IT 279, Chung-Chih Li41 Compare: for and while for (Initialization_action; Condition; Condition_update) { statement_list; } int n,f=1; cin >> n; for (i=2; i<=n; i++) { f *= i; } cout << “ The factorial of ” << n << “ is ” << f << “. ” ; i=2; while (i<=n) { f *= i; i++; } 123 for (Initialization_action; Condition; Condition_update) { statement_list; }

2/19/2016IT 279, Chung-Chih Li42 For Loop is not really a definite loop int n,i; n = 100; for (i=1; i <= n; i++) { statement_list; } int n,i; n = 100; i = 1; while (i <= n) { statement_list; i++; } v.s.

2/19/2016IT 279, Chung-Chih Li43 break and continue The break statement in a for/while loop will force the program to jump out of the for/while loop immediately. The continue statement in a for/while loop will force the program to update the loop condition and then check the condition immediately. for (Initialization_action; Condition; Condition_update) { statement_list; }

2/19/2016IT 279, Chung-Chih Li44 Nested loops (loop in loop) cin >> a >> b; for (int i = 0; i < a; i++) { for (int j=0; j<b; j++) { cout << “*”; } cout << endl; } ************* b a

2/19/2016IT 279, Chung-Chih Li45 Nested loops (2) int a,b; cin >> a >> b; for (int i = 0; i < a; i++) { for (int j=0; j<b; j++) { if (j > i) break; cout << “*”; } cout << endl; } * ** *** **** b a

2/19/2016IT 279, Chung-Chih Li46 Nested loops (3) * ** *** **** b a int a,b; cin >> a >> b; for (int i = 0; i < a; i++) { for (int j=0; j<b && j < i; j++) { cout << “*”; } cout << endl; } j <= i; if (j > i) break;

2/19/2016IT 279, Chung-Chih Li47 Nested loops (4) int a,b; cin >> a >> b; for (int i = 0; i < a; i++) { for (int j=0; j<b; j++) { if (j < i) cout << “ ”; else cout << “*”; } cout << endl; } ************* ************ *********** ********** b a =

2/19/2016IT 279, Chung-Chih Li48 Nested loops (5) int a,i,j; cin >> a; for (i = 0; i < a; i++) { for (j=0; j<a; j++) { if (j < a-i) cout << " "; else cout << "*"; } for (j=0; j<a; j++) { if (j > i) break; cout << "*"; } cout << endl; } * *** ***** ******* ********* ***********