I2204 ImperativeProgramming Semester: 1 Academic Year: 2018/2019 Credits: 5 Dr Antoun Yaacoub

Transcription

1 Lebanese University Faculty of Science Computer Science BS Degree I2204 ImperativeProgramming Semester: 1 Academic Year: 2018/2019 Credits: 5 Dr Antoun Yaacoub

2 I2204- Imperative Programming Schedule 08h00-09h40 09h50-11h30 12h00-13h40 14h00-15h40 Monday Tuesday Wednesday Thursday Friday Saturday I2204 B1 I1100 G6 / X5 Fixed I2204 Lab G1 I2204 Lab G2 I1100 G4 / X7 1 week over 2 I2204 B1 I1100 G6 / X4 1 week over 2 I1100 G4 / A3 fixed I2232 9h00-12h00 B1 2Computer Science BS Degree -Imperative Programming (I2204)

3 I Imperative Programming Grading Lab presence Lab exam / Lab Question Session 1 Session 2 0 pt for more than 3 absence 25 pts Partial 22 pts 22 pts 0 pt Final 53 pts 53 pts 75 pts Total 100 pts 3Computer Science BS Degree -Imperative Programming (I2204)

4 Dr Antoun Yaacoub Office Faculty of Science Section 1 Old Building 2nd floor Office 220 Websites antoun.yaacoub@ul.edu.lb contact@antoun.me 4Computer Science BS Degree -Imperative Programming (I2204)

5 5Computer Science BS Degree -Imperative Programming (I2204)

6 6Computer Science BS Degree -Imperative Programming (I2204) I Imperative Programming Prerequisite C language I1101 I2204 I2206 I3341

7 7Computer Science BS Degree -Imperative Programming (I2204)

8 LUCPC LCPC ACPC ICPC 8Computer Science BS Degree -Imperative Programming (I2204)

9 9Computer Science BS Degree -Imperative Programming (I2204)

10 Rule 1 Arrival on time Admission in class is allowed only within the first 2 minutes!! 10

11 Rule 2 Arrival on time Enter the classroom 2 minutes ahead!! 11

12 Rule 3 Do not talk to each other during class Do not talk while anyone (teacher/student)is speaking to the class. 12

13 Rule 4 Raise your hand Raise your hand if you have a question 13

14 Rule 5 Respect your classroom No smoking, eating or drinking during class 14

15 Rule 6 Electronics are prohibited 15

16 16

17 What happens if I don t respect the rules? 1. You will be asked to leave the classroom 2. You will be granted 1 absence on the lab 17

18 Dr Siba Haidar 18

19 Introduction 19

20 About this course prerequisites: I1 101 or old INFO203 Imperative Programming I 50 hours Resources available soon on 20

21 Course Objective The purpose of this module is to deepen the study of the imperative programming through the use of advanced aspects of the imperative language seen I1101. The student must be able to implement the concepts covered in this course to create an application solving a complex problem as modules. 21

22 Course outline recursive functions structures pointers & arrays linked lists input / outputs 22

23 Chapter 1 Recursion

24 Chapter Outline 1. Recall of functions 2. The memory state and function calls 3. Recursive functions, their types and rules 4. Direct and indirect recursions 5. Recursion vs. iteration 6. Common problems (factorial, Fibonacci,...) 7. The effectiveness of recursion 24

25 Recall of functions 25

26 Exercise 1 Write a C program which reads an integer number, calculates its double and displays it on the screen. 26

27 Exercise 2 Write a program which does the same as in exercise 1, But this time the program calls a function "fill" to read the number another function "doubleit" to calculate the double of the number 27

28 Exercise 3 Write a program which calls a function "fill10" to read 10 integers another function "avg" to calculate the average of the integers then displays the average on the screen 28

29 Recall how to give functions a type? what are the arguments used for? can we call any function in C from within any other function? can we define any function in C within any other function? what is the difference of parameter and arguments? 29

30 Parameter & Argument the termparameter refers to any declaration within the parentheses following the function name in a function declaration or definition; the termargument refers to any expression within the parentheses of a function call. 30

31 Definition & Declaration defining a function is where you actually provide a definition what the function actually does between { } int addtwo(int a, int b) { return a + b; } declaring a function is simply telling the compiler about the function int addtwo(int a, int b); you can also write int addtwo(int, int); 31

32 Example 32

33 Function call every function in C may be called from any other or itself each invocation of a function causes a new allocation of the variables declared inside it declarations had something missing keyword auto automatically allocated 33

34 The Keyword auto storage for auto variables automatically allocated on function entry automatically freed on function return 34

35 Rule 1 Arrival on time Admission in class is allowed only within the first 2 minutes!! 35

36 Rule 2 Arrival on time Enter the classroom 2 minutes ahead!! 36

37 Rule 3 Do not talk to each other during class Do not talk while anyone (teacher/student)is speaking to the class. 37

38 Rule 4 Raise your hand Raise your hand if you have a question 38

39 Rule 5 Respect your classroom No smoking, eating or drinking during class 39

40 Rule 6 Electronics are prohibited 40

41 41

42 What happens if I don t respect the rules? 1. You will be asked to leave the classroom 2. You will be granted 1 absence on the lab 42

43 The memory state and function calls 43

44 Exercise Draw the memory state of the exercises 1, 2 and 3 in order to have a closer look and understand what happens during a function call 44

45 Recursive functions, their types and rules 45

46 Recursion what is recursion? when one function calls ITSELF directly or indirectly. why learn recursion? new mode of thinking powerful programming tool divide-and-conquer paradigm 46

47 Recursion many computations are naturally selfreferential a directory contains files and other directories. Euclid's gcd algorithm quicksort algorithm linked data structures 47

48 Recursive Function a recursive function definition has one or more base cases, input(s) for which the function produces a result trivially (without recurring), and one or more recursive cases, input(s) for which the program recurs (calls itself). 48

49 Example : Factorial factorial function can be defined recursively by the equations 0! = 1 and, for all n > 0, n! = n(n 1)! Neither equation by itself constitutes a complete definition; the first is the base case, the second is the recursive case. Because the base case breaks the chain of recursion, it is sometimes also called the "terminating case". 49

50 Example : Factorial #include<stdio.h> int factorial(int n) { if(n==0) return 1; else return (factorial(n-1)*n); } void factorialtest() { int num=3,f; f=factorial(num); printf("factorial of %d = %d",num,f);} int main(){ factorialtest(); return 0; } 50

51 Test functions every time we write a function "anyfunction" we must write another void function to test it we call it "anyfunctiontest" same name with Test suffix the test function must not read inputs from the keyboard for not to waste time it provides static test values should try to cover all test cases 51

52 Types of recursion Direct Recursion A function is said to be direct recursive if it calls itself directly. Indirect Recursion A function is said to be indirect recursive if it calls another function and this new function calls the first calling function again. 52

53 Example Direct Recursion int fibo (int n) { if (n==1 n==2) return 1; else return (fibo(n-1)+fibo(n-2)); } 53

54 Example Indirect Recursion int func1(int n) { if (n<=1) return 1; else return func2(n); } int func2(int n) { return func1(n); } 54

55 Quick sort algorithm 55

56 Greatest Common Divisor find largest integer d that evenly divides into p and q example suppose p = 32 and q = 24 integers that evenly divide both p and q: 1, 2, 4, 8 d = 8 (the largest) how would you compute gcd? 56

57 Greatest Common Divisor find largest integer d that evenly divides into p and q 57

58 Greatest Common Divisor find largest integer d that evenly divides into p and q 58

59 Tracing Recursive Functions "winding" part recursion heads to base case "unwinding" part returns back to original call example a() calls b(), and b() calls c(), and c() calls d() winding d() done, it goes back to c(), to b(), to a() unwinding 59

60 Exercise A Write a program in C to calculate the sum of numbers from 1 to n using recursion. Test Data : Input the last number of the range starting from 1 : 5 Expected Output : The sum of numbers from 1 to 5 : 15 60

61 Exercise B Write a program in C to print the array elements using recursion. 61

62 Exercise C Write a program in C to count the digits of a given number using recursion. Test Data : Input a number : 50 Expected Output : The number of digits in the number is : 2 62

63 why this is wrong? int noofdigits(int n1) { static int ctr=0; if(n1!=0) { ctr++; noofdigits(n1/10); } return ctr; } 63

64 Exercise D Write a program in C to Check whether a given String is Palindrome or not. Input a word to check for palindrome : mom Expected Output : The entered word is a palindrome. 64

65 Tail Recursivity tail-recursive function no additional work after recursive call except return often require an additional parameter non tail-recursive functions after the recursive call there is still work to do 65

66 Tail Recursivity tail-recursive function no additional work after recursive call except return often require an additional parameter non tail-recursive functions after the recursive call there is still work to do 66

67 Exercise 4: Recursive Print is print a tail-recursive function? output? 67

68 Exercise 4: Recursive Print

69 Exercise 5 write a tail-recursive function produces the following output when called with parameter n=

70 Exercise 6 recursive function triangle of stars pointing up triangle(9); * *** ***** ******* ********* 70

71 Exercise 7 triangle of stars pointing down triangle(9); ********* ******* ***** *** * 71

72 Rule 1 Arrival on time Admission in class is allowed only within the first 2 minutes!! 72

73 Rule 2 Arrival on time Enter the classroom 2 minutes ahead!! 73

74 Rule 3 Do not talk to each other during class Do not talk while anyone (teacher/student)is speaking to the class. 74

75 Rule 4 Raise your hand Raise your hand if you have a question 75

76 Rule 5 Respect your classroom No smoking, eating or drinking during class 76

77 Rule 6 Electronics are prohibited 77

78 78

79 What happens if I don t respect the rules? 1. You will be asked to leave the classroom 2. You will be granted 1 absence on the lab 79

80 Exercise 8 tail recursive factorial function you can use a helper function a helper function??? 80

81 What are Helper Functions? Helper functions are useful when you want to extend the amount of parameters that a certain function takes in. Helper functions are generally used to make our lives easier. This occurs most often when working with recursion, especially if you want your function to be tail recursive. 81

82 Let s look again at Factorial #include<stdio.h> int factorial(int n) { if(n==0) return 1; else return (factorial(n-1)*n); } void factorialtest() { int num=3,f; f=factorial(num); printf("factorial of %d = %d",num,f);} int main(){ factorialtest(); return 0; } 82

83 the of tail recursion in its simplest form is to return the answer that we have accumulated throughout all of the function calls in the last frame. 83

84 We know that we can t do this while only taking in a single parameter, n, so we look to create a helper function. 84

85 Exercise 8 85

86 Exercise 9 write tail recursive function binary search inside sorted arrays find if n is there no return -1 yes return its first occurrence index 86

87 Exercise 9 binary search find if 3 is there

88 Fibonacci Numbers infinite series 0, 1, 1, 2, 3, 5, 8, 13, 21, 34,.. a natural for recursion 88

89 Solution? it takes a really long time to compute F(40). 89

90 F(40)=? Why Inefficient? F(39) is computed once F(38) is computed twice F(37) is computed 3 times F(36) is computed 5 times F(35) is computed 8 times... F(0) is computed 165,580,141 times. 90

91 Possible Pitfalls With Recursion recursion can take a long time if it needs to repeatedly recompute intermediate results 91

92 Exercise 10 can you write a better Fibonacci recursive function? tail-recursive? 92