Branching Algorithm & C Program Control

1. Algorithm and ProgrammingBranching Algorithm & C Program Control Dr. Ir. Riri Fitri Sari MM MSc International Class Electrical Engineering Dept University of Indonesia 23 February 2009

2. Branching • No every lines are executed • Only those that comply with the prerequisite (condition). • The prerequisite consists of operans which is connected to the relational and logical operators

3. Branching • Produce a boolean statement, with the value of true and false. • Using the command: if_then_else

4. Branching • Example : • 5 = 5  True • 3 > 5  False • 5 <> 3  True • (A>5) AND (B>10)  • True if both are true • (A>5) OR (B>10)  • True if both are true or one of the value is ture. START condition Statement 1 Statement 2 END

5. Branching • Sample case: The average of positive numbers. Aim : • To calculate the average of some numbers entered through the keyboard (ended with entrance of the null value) • To show the frequency of positive number, total, and the average.

6. Branching Algorithm development • Global Algorithm read (bil) while bil <> 0 do [added all the positive number and calculate the frequency of the positive number) read (bil) ewhile [write the frequency of the number, the total, and the average value]

7. Branching Algorithm development (cont’d) • Flowchart with the branching command if-then-eif

8. Branching Number> 0 yes no Total := Total + number n := n + 1

9. Branching Algorithm development (cont’d) • Modify the global algorithm • variable n and total must be emptied

10. Branching • If there is only the null number entered : • Before write command check if n=0. • If n=0 or no number entered except the end sign, do not perform the write command.

11. Branching Modification Algorithm : n := 0 total := 0 read (bil) while bil <> 0 do if bil > 0 then total := total + number n := n + 1 eif

12. Branching Modified algorithm: read (bil) ewhile if n <> 0 then write (n, total, total/n) eif

13. Branching • Sample case “The largest number” endData := 0 read (bil) while bil <> endData do [check if the number is the largest number from all of the read number, write if so] read (bil) ewhile [write the largest number]

14. Branching • Algorithm Development : EndData := 0 read (bil) while bil <> EndData do if bil > maks then maks := bil eif read (bil) ewhile write (maks) • Is it true ?

15. Branching • Discussion: • Variable maks should be given initial number to avoid mistakes. • Variabel maks should be filled in with the first number read from the keyboard.

16. Branching • Algorithm becomes : EndData := 0 read (bil) maks := bil while bil <> EndData do if bil > maks then maks := bil eif read (bil) ewhile write (maks)

17. Branching • How if the number entered is 0 ? What happened ? • Correction ?

18. Branching Example “Odd and Even numbers” • Aim: to make an algorithm which can state a number is odd or even.

19. Stages: • To define if a number is odd or even by dividing by 2 (mod) . • If the modulus is 0  Even number • If not 0  Odd number

20. Branching • Algorithm EndData : = 0 read(bil) while bil <> 0 do sisa :=bil mod 2 if sisa = 0 then write (‘even’) else write (‘odd’) eif read (bil) ewhile

21. Branching Example: “Square Root” • Aim : to write a program to calculate the square root of the quadratic equation, in which the coefficient is entered from keyboard.

22. Branching • Stages: • Select the wrong condition by checking the coefficient value. • To define the type of square root equation based on the equation.

23. Branching Algorithm: read(a) while a<>0 do read (b,c) d:=b^2-4*a*c continue

24. Branching if d<0 then {Calculate complex square root} p:= -b/(2*a) q: = abs (sqr(-d)/((2*a)) write (‘x1=‘, p, ‘+’, q, ‘i’) write (‘x2=‘, p, ‘-’, q, ‘i’) else continue

25. Branching {complex square root or not } if d=0 then {calculate twin square } x1:= -b/(2*a) x2 := x1

26. Branching else {Calculate not twin sqrt} x1:= (-b+sqr(d))/(2*a) x2 := (-b-sqr(d))/(2*a) eif write (‘x1=‘, x1) write (‘x2=‘,x2) eif read(a)

27. Chapter 4 – C Program Control Outline 4.1 Introduction 4.2 The Essentials of Repetition 4.3 Counter-Controlled Repetition 4.4 The for Repetition Statement 4.5 The for Statement: Notes and Observations 4.6 Examples Using the for Statement 4.7 The switch Multiple-Selection Statement 4.8 The do…while Repetition Statement 4.9 The break and continue Statements 4.10 Logical Operators 4.11 Confusing Equality (==) and Assignment (=) Operators 4.12 Structured Programming Summary

28. Objectives • In this chapter, you will learn: • To be able to use the for and do…while repetition statements. • To understand multiple selection using the switch selection statement. • To be able to use the break and continue program control statements • To be able to use the logical operators.

29. 4.1 Introduction • This chapter introduces • Additional repetition control structures • for • Do…while • switch multiple selection statement • break statement • Used for exiting immediately and rapidly from certain control structures • continue statement • Used for skipping the remainder of the body of a repetition structure and proceeding with the next iteration of the loop

30. 4.2 The Essentials of Repetition • Loop • Group of instructions computer executes repeatedly while some condition remains true • Counter-controlled repetition • Definite repetition: know how many times loop will execute • Control variable used to count repetitions • Sentinel-controlled repetition • Indefinite repetition • Used when number of repetitions not known • Sentinel value indicates "end of data"

31. 4.3 Essentials of Counter-Controlled Repetition • Counter-controlled repetition requires • The name of a control variable (or loop counter) • The initial value of the control variable • An increment (or decrement) by which the control variable is modified each time through the loop • A condition that tests for the final value of the control variable (i.e., whether looping should continue)

32. 4.3 Essentials of Counter-Controlled Repetition • Example: int counter = 1; // initialization while ( counter <= 10 ) { // repetition condition printf( "%d\n", counter ); ++counter; // increment } • The statement int counter = 1; • Names counter • Defines it to be an integer • Reserves space for it in memory • Sets it to an initial value of 1

33. fig04_01.c Program Output 1 2 3 4 5 6 7 8 9 10

34. 4.3 Essentials of Counter-Controlled Repetition • Condensed code • C Programmers would make the program more concise • Initialize counter to 0 • while ( ++counter <= 10 ) printf( “%d\n, counter );

35. fig04_02.c

36. 4.4 The for Repetition Statement

37. 4.4 The for Repetition Statement • Format when using for loops for ( initialization; loopContinuationTest; increment ) statement • Example: for( int counter = 1; counter <= 10; counter++ ) printf( "%d\n", counter ); • Prints the integers from one to ten No semicolon (;) after last expression

38. 4.4 The for Repetition Statement • For loops can usually be rewritten as while loops: initialization;while( loopContinuationTest ) { statement; increment;} • Initialization and increment • Can be comma-separated lists • Example: for (int i = 0, j = 0; j + i <= 10; j++, i++) printf( "%d\n", j + i );

39. 4.5 The for Statement : Notes and Observations • Arithmetic expressions • Initialization, loop-continuation, and increment can contain arithmetic expressions. If x equals 2 and y equals 10 for ( j = x; j <= 4 * x * y; j += y / x ) is equivalent to for ( j = 2; j <= 80; j += 5 ) • Notes about the for statement: • "Increment" may be negative (decrement) • If the loop continuation condition is initially false • The body of the for statement is not performed • Control proceeds with the next statement after the for statement • Control variable • Often printed or used inside for body, but not necessary

40. 4.5 The for Statement : Notes and Observations Establish initial value of control variable counter = 1 counter = 1 true counter <= 10 printf( "%d", counter ); counter++ Increment the control Determine if final false Body of loop variable value of control (this may be many variable has been statements) reached

41. fig04_05.c Program Output Sum is 2550

42. fig04_06.c (Part 1 of 2)

43. Year Amount on deposit 1 1050.00 2 1102.50 3 1157.63 4 1215.51 5 1276.28 6 1340.10 7 1407.10 8 1477.46 9 1551.33 10 1628.89 fig04_06.c (Part 2 of 2) Program Output

44. 4.7 The switch Multiple-Selection Statement • switch • Useful when a variable or expression is tested for all the values it can assume and different actions are taken • Format • Series of case labels and an optional default case switch ( value ){ case '1': actions case '2': actions default: actions } • break; exits from statement

45. true false true false . . . true false case a action(s) case z action(s) case b action(s) break break break default action(s) case b case a case z 4.7 The switch Multiple-Selection Statement • Flowchart of the switch statement

46. fig04_07.c (Part 1 of 3)

47. fig04_07.c (Part 2 of 3)

48. fig04_07.c (Part 3 of 3)

49. Enter the letter grades. Enter the EOF character to end input. a b c C A d f C E Incorrect letter grade entered. Enter a new grade. D A b ^Z Totals for each letter grade are: A: 3 B: 2 C: 3 D: 2 F: 1 Program Output

50. 4.8 The do…while Repetition Statement • The do…while repetition statement • Similar to the while structure • Condition for repetition tested after the body of the loop is performed • All actions are performed at least once • Format: do { statement; } while (condition );