1 / 67

Modular Programming With Functions

Modular Programming With Functions. 1. Divide and Conquer. 4.1 Modularity. How do you solve a big/complex problem? Divide it into small tasks and solve each task. Then combine these solutions. 2. 4.1 Modularity (cont’d).

miron
Download Presentation

Modular Programming With Functions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Modular Programming With Functions 1

  2. Divide and Conquer 4.1 Modularity • How do you solve a big/complex problem? • Divide it into small tasks and solve each task. Then combine these solutions. 2

  3. 4.1 Modularity (cont’d) • In C we use functions also referred to as modulesto perform specific tasks that we determined in our solution 3

  4. Advantages of using modules • Modules can be written and tested separately • Modules can be reused • Large projects can be developed in parallel • Reduces length of program, making it more readable • Promotes the concept of abstraction • A module hides details of a task • We just need to know what this module does • We don’t need to know how it does it 4

  5. 4.2 Programmer Defined Functions • Every C program starts with main()function • Additional functions are called or invoked when the program encounters function names • Functions could be • Pre-defined library functions (e.g., printf, sin, tan) or • Programmer-defined functions (e.g., my_printf, area) • Functions • Perform a specific task • May take arguments • May return a single value to the calling function • May change the value of the function arguments (call by reference) 5

  6. Function definition return_typefunction_name (parameters) { declarations; statements; } intmy_add_func(int a, int b) { int sum; sum = a + b; return sum; } 6

  7. Programmer-Defined Functions Terminology • Function Prototype describes how a function is called int my_add_func(int, int); • Function Call result = my_add_func(5, X); • Function implementation int my_add_func(int a, int b) { … } • Function parameters • Formal parameters • Actual parameter • Formal parameters must match with actual parameters in order, number and datatype. • If the type is not the same, type conversion will be applied (coercion of arguments). But this might cause some errors (doubleint) so you need to be careful! 7

  8. Example: Pre-defined Functions So far, we used several pre-defined functions! #include <stdio.h> #include <math.h> int main(void) { double angle; printf(“Input angle in radians: \n“); scanf(“%lf”, &angle); printf(“The sine of the angle is %f\n“, sin(angle) ); return 0; } double sin(double radian); double sin(double radian) { /* details of computing sin */ } 8

  9. Example: Programmer-defined Functions #include <stdio.h> int main(void) { double x1,y1,x2,y2, dist; printf(“Enter x1 y1 x2 y2 :”); scanf(“%lf %lf %lf %lf”, &x1,&y1,&x2,&y2); dist =sqrt(pow((x2-x1),2) + pow((y2-y1),2)); printf(“Distance is %lf\n”, dist); return 0; } #include <stdio.h> double distance(double, double, double, double); int main(void) { double x1,y1,x2,y2, dist; printf(“Enter x1 y1 x2 y2 :”); scanf(“%lf %lf %lf %lf”, &x1,&y1,&x2,&y2); dist = distance(x1,y1,x2,y2); printf(“Distance is %lf\n”, dist); return 0; } double distance(double x1, y1,x2,y2) { return sqrt(pow((x2-x1),2) + pow((y2-y1),2)); } 9

  10. Exercise (6,8) (-3,5) (4,-1) • Suppose you are given the coordinate points of a triangle as shown above, write a program that can find the length of each edge… • User enters: (x1, y1), (x2, y2), and (x3, y3) 10

  11. Value Returning Functions • Function returns a single value to the calling program • Function definition declares the type of value to be returned • A returnexpression; statement is required in the function definition • The value returned by a function can be assigned to a variable, printed, or used in an expression 11

  12. Void Functions • A void function may be called to • perform a particular task (clear the screen) • modify data • perform input and output • A void function does not return a value to the calling program • A return; statement can be used to exit from function without returning any value 12

  13. Exercise: void function #include <stdio.h> void print_i_star(int i); main() { int i; for (i=1; i<=5; i++) { print_i_star( i ); } } void print_i_star(int i) { int j; for (j=1; j<=i; j++) printf(“*”); printf(“\n”); return; } • Write a program to generate the following output? * ** *** **** ***** for (i=1; i<=5; i++) { for (j=1; j<=i; j++) printf(“*”); printf(“\n”); } 13

  14. Function name Return Type Parameter Declarations Declarations Statements Example: value returning function n!=n*(n-1)*…*1, 0! = 1 by definition int fact(int n) { int factres = 1; while(n>1) { factres = factres*n; n--; } return(factres); } 14

  15. Example – use fact() #include <stdio.h> int fact(int n); /* prototype */ int main(void) { int t= 5,s; s = fact(t) + fact(t+1); printf(“result is %d\n”, s); return 0; } Function call 15

  16. Example – execution of factorial function (cont’d) fact( 5 ) int fact(int n) { int factres = 1; while(n>1) { factres = factres*n; n--; } return(factres); } 16

  17. Example – execution of factorial function (cont’d) int fact(int n) { int factres = 1; while(n>1) { factres = factres*n; n--; } return(factres); } 17

  18. Example – execution of factorial function (cont’d) #include <stdio.h> int fact(int n); /* prototype */ int main(void) { int t= 5,s; s = 120 + fact(t+1); printf(“result is %d\n”, s); return 0; } Function call 18

  19. Example – execution of factorial function (cont’d) fact( 6 ) int fact(int n) { int factres = 1; while(n>1) { factres = factres*n; n--; } return(factres); } t+1 19

  20. Example – execution of factorial function (cont’d) int fact(int n) { int factres = 1; while(n>1) { factres = factres*n; n--; } return(factres); } 20

  21. Example – execution of factorial function (cont’d) #include <stdio.h> int fact(int n); /* prototype */ int main(void) { int t= 5,s; s = 120 + 720; printf(“result is %d\n”, s); return 0; } result is 840 21

  22. Example – reuse of factorial function • Write a statement to compute Enter X, Z, K, D … y=(fact(X)+fact(Z)*5)/(fact(K)-fact(D)); 22

  23. Example – reuse of factorial function in another function • Write a select function that takes n and k and computes “n choose k” where int select(int n, int k) { return fact(n)/(fact(n-k)*fact(k)); } 23

  24. Function Examples 24

  25. Exercise • Write a function to compute maximum and minimum of two numbers int max(int a, int b) { if (a > b) return a; else return b; } int min(int a, int b) { if (a < b) return a; else return b; } 25

  26. Exercise • Are following calls to max function valid? • What will be the result? int max(int a, int b); int min(int a, int b); int main() { int x = 2, y = 3, z = 7, temp; temp = max(x,y); temp = max(4,6); temp = max(4,4+3*2); temp = max(x,max(y,z)); } 26

  27. Example for void function void print_date(int mo, int day, int year) { /*output formatted date */ printf(“%i/%i/%i\n”, mo, day, year ); return; } 27

  28. Exercise • Write a function that takes score as parameter and computes and returns letter grade based on the scale below. 80-100 A 60-79 B 40-59 C 0-39 D 28

  29. Solution char get_letter_grade(int score) { char grade; if ((score >= 80) && (score <=100)) grade = 'A'; else if ((score >= 60) && (score <= 79)) grade = 'B'; else if ((score >= 40) && (score <= 59)) grade = 'C'; else if ((score >= 0) && (score <= 39)) grade = 'D'; return grade; } 29

  30. Exercise • Write a function to compute logba double log_any_base(double a, double b) { return log(a)/log(b); } 30

  31. Exercise: Trace functions • What is the output of the following program #include <stdio.h> int function1(int x) { x = 2; printf("Out1 = %d\n",x); return(x+1); } int main() { int x = 4, y; y = function1(x); printf("Out2 = %d\n",x); printf("Out3 = %d\n",y); return 0; } Output Out1 = 2 Out2 = 4 Out3 = 3 31

  32. Exercise • What is the output of the following program #include <stdio.h> void function2() { printf("In function 2\n"); } void function1() { function2(); printf("In function 1\n"); } void function3() { printf("In function 3\n"); function2(); } int main() { function1(); function3(); return 0; } Output In function 2 In function 1 In function 3 In function 2 32

  33. Parameter Passing • Call by value • formal parameter receives the value of the actual parameter • function can NOT change the value of the actual parameter (arrays are an exception) • Call by reference • actual parameters are pointers (ch 5 and 6) • function can change the value of the actual parameter 33

  34. Scope of a function or variable • Scope refers to the portion of the program in which • It is valid to reference the function or variable • The function or variable is visible or accessible #include <stdio.h> int fact(int n); /* prototype */ int main(void) { int t= 5,s; s = fact(t) + fact(t+1); printf(“result is %d\n”, s); return 0; } int fact(int n) { int factres = 1; while(n>1) { factres = factres*n; n--; } return(factres); } 34

  35. Scope of a function or variable • Same variable name can be used in different functions #include <stdio.h> int fact(int n); /* prototype */ int main(void) { int t= 5,s; s = fact(t) + fact(t+1); printf(“result is %d\n”, s); return 0; } int fact(int t) { int s = 1; while(t>1) { s = s*t; t--; } return(s); } 35

  36. Scope • Local scope • a local variable is defined within a function or a block and can be accessed only within the function or block that defines it • Global scope • a global variable is defined outside the main function and can be accessed by any function within the program file. 36

  37. Global vs Local Variable #include <stdio.h> int z = 2; void function1() { int a = 4; printf("Z = %d\n",z); z = z+a; } int main() { int a = 3; z = z + a; function1(); printf("Z = %d\n",z); z = z+a; return 0; } Output Z = 5 Z = 9 37

  38. Storage Class - 4 types Storage class refers to the lifetime of a variable • automatic - key word auto - default for local variables • Memory set aside for local variables is not reserved when the block in which the local variable was defined is exited. • external - key word extern - used for global variables • Memory is reserved for a global variable throughout the execution life of the program. • static - key word static • Requests that memory for a local variable be reserved throughout the execution life of the program. The static storage class does not affect the scope of the variable. • register - key word register • Requests that a variable should be placed in a high speed memory register. 38

  39. void fun () { int a=6; a = a + 1; printf ("\nInside fun a = %d ", a); } void fun1 () { static int a; a = a + 1; printf ("\nInside fun1 a = %d ", a); } void fun (void); void fun1 (void); void fun2 (void); int count1=20; int main () { int count=5; fun (); fun (); fun1 (); fun1 (); fun2 (); fun2 (); printf ("\nIn main count = %d count1 = %d\n\n",count, count1); return 0; } void fun2 () { int count=10; count = count + 1; count1 = count1 + 1; printf ("\nInside fun2 count = %d count1=%d ", count, count1); }

  40. 4.4 Random Numbers • What is a random number? • Tossing a coin (0, 1) Rolling a die (1, 2,…6) • Min, Max, Avg, possible outcomes are equally likely or not, • Engineering problems require use of random numbers • How can you compute the area of an irregular shape? 41

  41. Uniform Random numbers • All outcomes are equally likely • For example fair die, where each outcome has the same probability of 1/6, • So we can generate uniform random numbers between 1 and 6 by rolling a die. • What if we need random numbers in another range? For example, 1 and 100? 42

  42. Uniform Random numbers (cont’d) • In Standard C library, we have a function rand() to generate random numbers between 0 and RAND_MAX • RAND_MAX is a system dependent constant (e.g., 32,767) defined in stdlib.h • What will be the output of the following printf(“%d %d %d\n”,rand(), rand(), rand()); • What will be the output, if we re-run the same program? 43

  43. Pseudo-random Numbers • Computers generate random numbers using a seed number and an algorithm. • So, if you give the same seed, you will always get the same sequence of pseudo-random numbers • In Standard C library, we have a function srand(int seed) to give a new seed number 44

  44. Example: generate 10 RNs #include <stdio.h> #include <stdlib.h> int main(void) { /* Declare variables. */ unsigned int seed; int k; /* Get seed value from the user. */ printf("Enter a positive integer seed value: \n"); scanf("%u",&seed); srand(seed); /* Generate and print ten random numbers. */ printf("Random Numbers: \n"); for (k=1; k<=10; k++) printf("%i ",rand()); printf("\n"); /* Exit program. */ return 0; } 45

  45. RNs in a specified range [a b] • Generate a RN between 0 and 7 x = rand() % 8; • Generate a RN between 10 and 17 x = 10 + rand() % 8; int rand_int(int a,int b) { return rand()%(b-a+1) + a; } 46

  46. Floating-Point RNs in a specified range [a b] • x = rand() / RAND_MAX will give a random number between 0.0 and 1.0 • x = rand() / RAND_MAX *(b-a) will give a RN between 0.0 and b-a • The value is then shifted into range [a b] by adding a double rand_float(double a,double b) { return ((double)rand()/RAND_MAX)*(b-a)+a; } 47

  47. Example: HiLo Game /* Write a program that allows a user to play HiLo game. User wins if he/she can guess the number between 1-100 within at most 6 iterations */ #include <stdio.h> #include <stdlib.h> int rand_int(int a,int b); /* prototype */ void playHiLo( int s); int main(void) { unsigned int seed; /* Declare variables */ int secret; printf("Enter a positive integer seed value: \n"); scanf("%u",&seed); srand(seed); while(1){ secret = rand_int(1,100); playHiLo(secret); } return 0; } 48

  48. int rand_int(int a,int b) { return rand()%(b-a+1) + a; } void playHiLo(int s) { int i, guess; for(i=1; i <=6; i++){ printf("Enter your guess : "); scanf("%d", &guess); if (guess > s) printf("It is Higher than secret\n"); else if (guess < s) printf("It is Lower than secret\n"); else { printf("Cong! you won\n"); return; } } printf("Sorry! Try again\n"); return; } 49

  49. Exercise: Another “guess the number game” • Computer selects a random number s between [1000 9999] • User tries to guess it by entering g • Computer tells how many digits are in place, out of place, not in secret number • For example, if s is 6234 • User enters g as 7436, then computer says • 1 digit is in place • 2 digits are out of place • 1 digit is not in secret number • User keeps trying until he finds the secret number 50

More Related