1. Outlines Chapter 3 –Chapter 3 – Loops & Revision –Loops while do … while – revision 1

2. The while loops 2

3. 3 The for loop does something a fixed number of times. What happens if you don’t know how many times you want to do something before you start the loop? In this case a different kind of loop may be used: the while loop.

4. The while loops while (expression) statement(s) non-zero value (true) A while loop will continue executing as long as expression evaluates to a non-zero value (true). 4

5. Example 1 5 Asks the user to enter a series of numbers. When the number entered is 0, the loop terminates. Notice that there’s no way for the program to know in advance how many numbers will be typed before the 0 appears; that’s up to the user.

6. Example 1, cont. 6 // endon0.cpp // demonstrates WHILE loop #include using namespace std; int main() { int n = 99; // make sure n isn’t initialized to 0 while( n != 0 ) // loop until n is 0 cin >> n; // read a number into n cout << endl; return 0; }

7. The syntax of the while loop 7 The while loop looks like a simplified version of the for loop. It contains a test expression but no initialization or increment expressions.

8. Multiple Statements in a while Loop 8 Example 2:Example 2: calculates the fourth power of a series of integers. Let’s assume that in this program it’s important to put the results in a column four digits wide. To ensure that the results fit this column width, we must stop the loop before the results become larger than 9999. Without prior calculation we don’t know what number will generate a result of this size, so we let the program figure it out.

9. Multiple Statements in a while Loop, cont. 9 #include #include //for setw using namespace std; int main() { int pow=1; //power initially 1 int numb=1; //numb goes from 1 to ??? while( pow<10000 ) //loop while power <= 4 digits { cout << setw(2) << numb; //display number cout << setw(4) << pow << endl; //display fourth power ++numb; //get ready for next power pow = numb*numb*numb*numb; //calculate fourth power } cout << endl; return 0; }

10. Multiple Statements in a while Loop, cont. 10 Here’s the output:1 2 16 3 81 4 256 5 625 6 1296 7 2401 8 4096 9 6561

11. The precedence of the operators 11

12. while statement equivalent to for statement 12 The general form of the for statement is for ( initialization; loopContinuationCondition; increment ) statement In most cases, the for statement can be represented by an equivalent while statement, as follows: initialization; while ( loopContinuationCondition ) { statement increment; }

13. while statement equivalent to for statement, cont. How do you print your name 10 times using a while loop? int x = 0; while (x < 10) { cout << “Ahmed” << endl; x++; } 13

14.  Write a program for computing factorial N (N!), Where N! = 1 *2 * 3 * N. #include using namespace std; void main() { int N; cout<<"Please enter a number:"; cin>>N; int f = 1; for(int i = N; i>1; i--) f = f * i; cout<<"Factorial of "<<N<<" is "<<f<<endl; }

15. #include using namespace std; void main() { int N; cout<<"Please enter a number:"; cin>>N; int f = 1; int i = N; while(i>1) { f = f * i; i--; } cout<<"Factorial of "<<N<<" is "<<f<<endl; }

16. The Do..while loops 16

17. Control Structures--do…while loops 17 A do..while loop is very similar to a regular while loop. Terminating condition is specified at the end of the loop do { statements; } while (expression);

18. Syntax of do..while 18

19. Example 4 19 DIVDO, invites the user to enter two numbers: a dividend (the top number in a division) and a divisor (the bottom number). It then calculates the quotient (the answer) and the remainder, using the / and % operators, and prints out the result.

20. Example 4, cont. 20 #include using namespace std; void main() { long dividend, divisor; char ch; do //start of do loop { //do some processing cout > dividend; cout > divisor; cout << “Quotient is “ << dividend / divisor; cout << “, remainder is “ << dividend % divisor; cout << “\nDo another? (y/n): “; //do it again? cin >> ch; } while( ch != ‘n’ ); //loop condition }

21. Example 4, cont. 21 Here’s an example of DIVDO’s output: Enter dividend: 11 Enter divisor: 3 Quotient is 3, remainder is 2 Do another? (y/n): y Enter dividend: 222 Enter divisor: 17 Quotient is 13, remainder is 1 Do another? (y/n): n

22. Revision 22

23. Questions 1- Convert each of the following mathematical formulas to a C++ expression. 2- The following code intends to input a user’s first name, last name, and age. However, it has an error. Fix the code. string fullName; int age; cout << "Enter your first and last name." << endl; cin >> fullName; cout << "Enter your age." << endl; cin >> age; cout << "You are " << age << " years old, " << fullName << endl;

24. Questions cont., 3- What will the following code output? {string s1 = "5"; string s2 = "3"; string s3 = s1 + s2; cout << s3 << endl;} 4- Determine the value, true or false, of each of the following Boolean expressions, assuming that the value of the variable count is 0 and the value of the variable limit is 10. Give your answer as one of the values true or false. »a. (count = = 0) && (limit < 20) »b. count = = 0 && limit < 20 »c. (limit > 20) || (count < 5) »d. !(count = = 12) »e. (count = = 1) && (x < y) »f. (count < 10) || (x < y) »g. !( ((count = 0) ) »h. ((limit / count) > 7) || (limit < 20) »i. (limit 7) »j. ((limit / count) > 7) && (limit < 0) »k. (limit 7) ) + (!6)

25. Questions cot., 5- Does the following sequence produce division by zero? { j = -1; if ((j > 0) && (1/(j + 1) > 10)) cout << i << endl; } 6- Write an if-else statement that outputs the word Warning provided that either the value of the variable temperature is greater than or equal to 100, or the value of the variable pressure is greater than or equal to 200, or both. Otherwise, the if-else statement outputs the word OK. The variables temperature and pressure are both of type int.

26. Questions cont., 7- What is the output of the following? Explain your answers. a. if(0) cout << "0 is true"; else cout << "0 is false"; cout << “ try again”; b. if(1) cout << "1 is true"; else cout << "1 is false"; cout << “ try again”; c. if(-1) cout << "-1 is true"; else {cout << "-1 is false"; cout << “ try again”;}

27. Questions cont., 8- What output will be produced by the following code? int x = 2; cout << "Start\n"; if (x <= 3) if (x != 0) cout << "Hello from the second if.\n"; else cout << "Hello from the else.\n"; cout << "End\n"; cout << "Start again\n"; if (x > 3) if (x != 0) cout << "Hello from the second if.\n"; else cout << "Hello from the else.\n"; cout << "End again\n";

28. Questions cont., 9- Write a multi-way if-else statement that classifies the value of an int variable n into one of the following categories and writes out an appropriate message. n 100 10- What is the output of the following? int count = 3; while (count- - > 0) cout << count << " "; 11. What is the output of the following? int count = 3; while (- -count > 0) cout << count << " "; 12. What is the output of the following? int n = 1; do cout << n << " "; while (n++ <= 3);

29. Answers 1- 3*x + y, (x + y)/7 Note that x + y/7 is not correct, (3*x + y)/(z + 2) 2- the fixed program will be { string first, last; int age; cout << "Enter your first and last name." << endl; cin >> first >> last; cout << "Enter your age." << endl; cin >> age; cout << "You are " << age << " years old, " << first << " " << last << endl;} 3- 53 4- true, true, true, true, false, true, false, error ((limit/count) > 7) involves a division by zero, true, error (division by zero), false, true. 5- no, since j>0 is false condition. 6. if ( (temperature >= 100) || (pressure >= 200) ) cout << "Warning"; else cout << "OK";

30. Answers 7- All nonzero integers are converted to true ; 0 is converted to false. a. 0 is false try again b. 1 is true try again c. -1 is true 8- Start Hello from the second if. End Start again End again 9- Both of the following are correct if (n < 0) cout << n << " is less than zero.\n"; else if ((0 <= n) && (n <= 100)) cout << n << " is between 0 and 100\n"; else if (n >100) cout << n << " is larger than 100.\n"; if (n < 0) cout << n << " is less than zero.\n"; else if (n <= 100) cout << n << " is between 0 and 100.\n"; else cout << n << " is larger than 100.\n";

31. Answers 10- 2 1 0 11- 2 1 12- 1 2 3 4

32. Lecture 7

33. Selection Structure 33

34. Flow of Control Statements Three kinds of control structures 1.Sequential Structure 2.Repetition structure (also known as Iterative or Loops ) –For –While –do-while 3.Selection structure (also known as Decisions or Branches ) – if –if-else –Switch 34

35. Selection Structure 35 C++ provides three types of selection statements: 1.The if selection statement either performs (selects) an action if a condition (predicate) is true or skips the action if the condition is false. 2.The if … else selection statement performs an action if a condition is true or performs a different action if the condition is false. 3.The switch selection statement performs one of many different actions, depending on the value of an integer expression.

36. Precedence: Arithmetic and Relational Operators 36 Example 3:Example 3: Fibonacci series, the first few terms of the series are: 1 1 2 3 5 8 13 21 34 55 Each term is found by adding the two previous ones: 1+1 is 2, 1+2 is 3, 2+3 is 5, 3+5 is 8, and so on.

37. Precedence: Arithmetic and Relational Operators, cont. 37 #include using namespace std; int main() { //largest unsigned long const unsigned long limit = 4294967295; unsigned long next=0; //next-to-last term unsigned long last=1; //last term while( next < limit / 2 ) //don’t let results get too big { cout << last << “ “; //display last term long sum = next + last; //add last two terms next = last; //variables move forward last = sum; // in the series } return 0; }

38. Precedence: Arithmetic and Relational Operators, cont. 38 The test expression uses two operators: (next < limit / 2) Our intention is to compare next with the result of limit/2. higherarithmetic operators have a higher precedence than relational operators.

39. Nesting If Statement & Loops 39

40. Nesting: ifs Inside Loops The loop and decision structures we’ve seen so far can be nested inside one another. You can nest ifs inside loops, loops inside ifs, ifs inside ifs, and so on. Example 6, PRIME. –This example tells you whether a number you enter is a prime number. –Prime numbers are integers divisible only by themselves and 1. The first few primes are 2, 3, 5, 7, 11, 13, 17.

41. Nesting ifs Inside Loops, cont. #include using namespace std; #include //for exit() int main() { unsigned long n, j; cout << “Enter a number: “; cin >> n; //get number to test for(j=2; j <= n/2; j++) //divide by every integer from if(n%j == 0) //2 on up; if remainder is 0, {cout << “It’s not prime; divisible by “ << j << endl; exit(0); //exit from the program } cout << “It’s prime\n”; return 0; }

42. Nesting ifs Inside Loops, cont. Here’s output from three separate invocations of the program: Enter a number: 13 It’s prime Enter a number: 22229 It’s prime Enter a number: 22231 It’s not prime; divisible by 11

43. Your Turn 43

44. Your Turn (1/2) 44 10. Write a while loop that displays the numbers from 100 to 110. 11. True or false: Relational operators have a higher precedence than arithmetic operators. 13. Write a do loop that displays the numbers from 100 to 110.

45. Your Turn (2/2) 45 14. Write an if statement that prints Yes if a variable age is greater than 21. 15. The library function exit() causes an exit from a. the loop in which it occurs. b. the block in which it occurs. c. the function in which it occurs. d. the program in which it occurs.

46. H.W. 46 Write a program that uses a while statement to calculate the factorial. The FACTOR program asks the user to type in a number, and then calculates the factorial of this number. The factorial is calculated by multiplying the original number by all the positive integers smaller than itself. Thus the factorial of 5 is 5*4*3*2*1, or 120.

47. Thanks 47