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1 Introduction to Programming ( 數 ) Lecture 5 Spring 2005 March 25, 2005 Topics Review Loop Statements For-Loop Condition-Loop Arrays: Part I Function Definition: Part I 1

2 Review of Loop Statements (Repetition statements, Loop, Iteration ): ( ) 行 C Loop statements for loop: (Counting loop) while loop: (Condition loop) do-while loop: (Condition loop) while loop Syntax for while loop while ( expr ) { statements; } next-statements; Condition: true of false expr: children = 7; cookies = 1; while ( children > 0 ) { children = children - 1 ; cookies = cookies * 2 ; } 2

3 while loop Flow chart for while loop expr false true statements Note: C has no boolean value; C uses int for boolean values 0 for false and non-zero for true next-statements The do-while Repetition Structure do { statement(s) } while ( condition ) ; The body of a do-while is ALWAYS executed at least once. 3

4 for for (for loop) for ( expr1 ; expr2 ; expr3 ) { statements; } next-statements; 數行數 --for (for loop) 流 for 流 expr1 expr2 false true statements expr3 next-statements 4

5 Arrays 列 : Part I 料類數量 Arrays Assignment 2, 12 數來數什不數數, 理料 ( 料 ), 數來料, 不數來料, 數量, 來不便 C 了料列 (Array) 列, 數, 更易讀 Instead of defining 12 variables, such as jan, feb,, dec, we define an array: int num_of-days[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31} ; 5

6 Array 列說數, 列串連數列, 了數數, 列, 便料列列列 (Array) 列 (Array) 列 6

7 列 (Array) 列列量 (Capacity, size), 列 " " 料, 列數列料, 列連列索 (index), 讀, 索 0~size-1 array bound range 列 (Array) 列, 數, [ ], 列量, 列列例 7

8 列 (Array) 料列料, 列, int char float double, 列數, 不列量數列列數列料, 列, 料列索 ( ) 0, 例 10 列, 列 0~9 列列 [ ] 例 int ID [10]; 列, 10 ID [0] ID [1] ID [2]... ID [9] 8

9 Array Declarations Revisited int numbers[5] ; This declaration sets aside a chunk of memory that is big enough to hold 5 integers. Besides the space needed for the array, there is also a variable allocated that has the name of the array numbers. This variable holds the address of the beginning (address of the first element) of the array. numbers FE00 FE Array Name Holds an Address #include <stdio.h> int main( ) { int numbers[5] = {97, 68, 55, 73, 84} ; // } printf ( numbers[0] = %d\n, numbers[0]) ; printf ( numbers = %X\n, numbers) ; printf ( &numbers[0] = %X\n, &numbers[0]) ; return 0 ; output numbers[0] = 97 numbers = FE00 &numbers[0] = FE00 numbers &numbers[0] 9

10 How Indexing Works int numbers[5] ; Assuming a 4-byte integer, Location of numbers[2] = FE00 + (2 * 4) numbers FE00 FE00 FE04 FE08 FE0C FE Index: 列, 數列, 列 1. 列量數 2. 列 0 3. 數列量 10

11 1. 列量數列 int a [n], 列 n 數數, 列 0 ~ n-1 例列 11

12 行 2. 列 0 數列量, 不 0 a [0] 0, a [1] ~ a [4], 0 12

13 3. 數列量例 13

$i; scanf( Please input i: \n, &i); answer[i] =? ; 14$

14 行列數料列, 不列量 Array out of bound error; C 不類 int i; scanf( Please input i: \n, &i); answer[i] =? ; 14

15 Array Bounds Checking C has no range checking when working with arrays, so if you use a subscript value past the end of the array, it will not tell you about it. It will eventually crash or give you garbage data. int main( ) { int i, b[5] = { 0, 1, 2, 3, 4}; for (i=0; i<6; i++) printf("%3d", b[i]); garbage return 0; } Output: 列,, 列量, 列, 不列 0, 1 理列,, 15

16 了數, 理列 # define 數來列量年料 16

17 年料行 17

18 列列來理 " 列 " 料, 數列, 列, 列數, 列列列數數列 Ex: 列列數, 利列 [0] 18

19 5 列 5 列 19

20 行行, 來, 列 Ex: 列列,, 例來例, 列 20

21 5 數數 5 數數 21

22 5 數數行 22

23 Ex: 數列 (Search), 列料, 列, 便料例, 數, 數列列料 23

24 列料行 24

25 列列說列, Index starts from 0! 25

26 列列, 列列行兩,,, 料行列數列量行列列, 行列, 列 26

27 行列 " 列 " " 行 ", 列料列料 27

28 列料行 28

29 行列列數列, 列 4, " 列 " 數, 兩列,, 易度, 讀行易理數列量列, 量, 列數, 列度, 料列 29

30 數列量行數, 列數,, 列數行數, 列 (2D Array) 料列列數行數例 int num[2][2]; /* 2x2 列 */ col 1 col 2 Row-major row 1 num[0][0] num[0][1] m num[0][0] row 2 num[1][0] num[1][1] m+4 num[0][1] m+8 num[1][0] m+12 num[1][1] Num[1, 1] is wrong! Row-major vs. Column-major 30

31 列列列, 不, 行數列 Ex: 列 (2D Array) 例 3*4 列, 來. void main( ) { int x[3][4]; int i,j; printf( Please input 2 dimension array(3*4).\n ); for ( i = 0; i < 3; i++ ) for ( j = 0; j < 4; j++ ) scanf( %d,&x[i][j]); } printf( The result 2 dimension array is as following : \n ); for ( i = 0; i < 3; i++ ) { for ( j = 0; j < 4; j++ ) printf( %3d, x[i][j]); printf( \n ); } 31

32 Ex: 列利列來兩列 A 列 B, 列 C 兩列, 兩列, 兩 A B C 列 32

33 列兩列 33

34 兩列兩列 34

35 兩列行 35

36 Functions: I (Programmer-Defined Functions) Using Functions in C A C program is made up of one or more functions, one of which is main( ). Execution always begins with main( ). A function is a sub-unit of a program which performs a specific task. (sub-program) Library functions (e.g., printf) Programmer-Defined Functions Using functions: call (invoke) a function 36

$\n ) ; this statement is return 0 ; is known as a } function call this is a string we are passing as an argument (parameter) to Argument: 數 the printf function Parameter: 參數 Functions as Black Boxes;$

37 Sample Function Call #include <stdio.h> int main ( ) printf is the name of a predefined { function in the stdio library printf ( Hello World!\n ) ; this statement is return 0 ; is known as a } function call this is a string we are passing as an argument (parameter) to Argument: 數 the printf function Parameter: 參數 Functions as Black Boxes; Code Reuse & Functional Abstractions Figure 3.6 Function sqrt as a Black Box 37

38 Syntax of Function Call Function name Argument(s) [Actual Parameter(s)] argument function call y = sqrt( 16 ) ; function name Argument (actual parameter) Function call may return a value. y 04 More Function Call Examples printmessage() // no argument sqrt( x ) sqrt( x+y) pow(2, 3) // two arguments; order! three(x, y*z, -5) nested(2*x, fun(y, 1), 0) pow(2, 3) <> pow(3, 2) 38

39 Some C Library Functions Standard IO (<stdio.h> printf, scanf, etc. Mathematical Functions <math.h> and <stdlib.h> abs(x) // <stdlib.h> ceil(x) floor(x) exp(x) sqrt(x) pow(x, y) cos(x) z = (x-y)3 Examples z = sqrt(pow(x-y,3)) Figure 3.8 Triangle with Unknown Side a a 2 = b 2 + c 2 2 b c cos a = sqrt( pow(b, 2) + pow(c, 2) 2*b*c*cos(alpha*PI / 180.0)) 39

40 Programmer-Defined Functions Programmers can write their own functions. C function names follow the same naming rules as C variables. /* Input: two integers * Output: the maximum of the input; if the * input are equivalent, return the 2nd integer */ int maximum (int a, int b) { if (a > b) return a; else return b; } Declaring Functions Requires prototype & function itself Prototype (before function itself) Tells compiler number & type of arguments passed in Type of value returned E.g., int maximum (int, int); or int maximum (int a, int b); /* a & b are ignored by the compiler */ 40

41 Declaring Functions, Cont d Requires prototype & function itself Function itself Format: type function_name (parameter list); Parameter list type and name Must return a value of specified type unless type is void int maximum (int a, int b) { Formal parameters: a and b if (a > b) return a; else return b; } Example Use of a Function (Must be declared before it is used) #include <stdio.h> int maximum (int, int); function prototype void main () { int x, y, z; } printf ( Enter 2 intergers: ); scanf ( %d %d, &x, &y); z = maximum(x,y); printf( \nthe maximum is %d\n,z); function call int maximum (int a, int b) function header { if (a > b) return a; else function body return b; } function definition (declaration) 41

42 8 數, 數, 來說不, ifelse, 7 if-else 8 數, 8 數 42

43 8 數 8 數 43

44 行, 行兩數, 老老,, 44

45 8 數 8 數 45

46 compare 行 46

47 ,, 例 29~31 行, compare ( ) compare ( ) ( 例 main ( ) compare ( ) ), 47

48 Semantics of Function Call When program control encounters a function name, the function is called (invoked). Program control passes to the function. The function is executed. Control is passed back to the calling function with the possible return value. main fun1 fun2 fun1(); fun2(); 論, 了 48

49 , 數數 49

50 main ( ) Functions without Arguments Without Return Values #include <stdio.h> void printmessage ( void ) ; int main ( ) { printmessage ( ) ; return 0 ; } void printmessage ( void ) { printf ( A message for you:\n\n ) ; printf ( Have a nice day!\n ) ; } return 50

51 void functions A function doesn't have to take or return arguments. We prototype such a function using void. Prototype (at top of file remember) void print_hello (void); void print_hello (void) /* this function prints hello */ { printf ("Hello\n"); } void odd_or_even (int); void odd_or_even (int num) /* this function prints odd or even appropriately */ { if ((num % 2) == 0) { } printf ("Even\n"); return; } printf ("Odd\n"); Function takes and returns void (no arguments) Another prototype Function which takes one int arguments and returns none Functions can call other functions Once you have written a function, it can be accessed from other functions. We can therefore build more complex functions from simpler functions int max_of_three (int, int, int); /* Prototype*/.. /* Main and rest of code is in here */. int max_of_three (int i1, int i2, int i3) /* returns the maximum of three integers */ { return (maximum (maximum(i1, i2), i3)); } 51

52 Local Variables in a Function type functionname ( parameter 1,..., parameter n ) { (local) variable declaration(s) statement(s) } If there are no parameters, either functionname( ) OR functionname(void) is acceptable. There may be some local variable declarations. If the function type (return type) is void, a return statement is not required, but the following are permitted: return ; OR return( ) ; Example of Local Variables local variable declaration int max_of_three (int a, int b, int c) { int tmp; if (a > b) tmp = a; else tmp = b; } if (tmp > c) return tmp; else return c; 52

53 Ex: 兩數數不, 兩數 53

54 Parameter Passings 參數 Actual parameters (arguments) are the parameters that appear in the function call. average = averagetwo (value1, value2) ; Formal parameters are the parameters that appear in the function header. float averagetwo (int num1, int num2) Actual and formal parameters are matched by position. Each formal parameter receives the value of its corresponding actual parameter. Parameter Passing (con t) Corresponding actual and formal parameters do not have to have the same name, but they may. Corresponding actual and formal parameters must be of the same data type, with some exceptions. 54

55 Local Variables Functions only see (have access to) their own local variables. This includes main( ). Formal parameters are declarations of local variables. The values passed are assigned to those variables. Other local variables can be declared within the function body. Parameter Passing and Local Variables #include <stdio.h> float averagetwo (int num1, int num2) float averagetwo (int num1, int num2) ; { int main ( ) float average ; { float ave ; average = (num1 + num2) / 2.0 ; int value1 = 5, value2 = 8 ; return average ; } ave = averagetwo (value1, value2) ; printf ( The average of ) ; printf ( %d and %d is %f\n, value1, value2, ave) ; return 0 ; } value1 value2 ave num1 num2 average 5 8 int int float int int float 55

56 Same Name, Still Different Memory Locations #include <stdio.h> float averagetwo (int num1, int num2) float averagetwo (int num1, int num2) ; { int main ( ) float average ; { float average ; average = (num1 + num2) / 2.0 ; int num1 = 5, num2 = 8 ; return average ; } average = averagetwo (num1, num2) ; printf ( The average of ) ; printf ( %d and %d is %f\n, num1, num2, average) ; return 0 ; } num1 num2 average num1 num2 average 5 8 int int float int int float Changes to Local Variables Do NOT Change Other Variables with the Same Name #include <stdio.h> void addone (int num1) ; void addone (int num1) { int main ( ) num1 = num1+1 ; { printf ( In addone: ) ; int num1 = 5 ; printf ( num1 = %d\n, num1) ; addone (num1) ; } printf ( In main: ) ; printf ( num1 = %d\n, num1) ; return 0 ; } num1 num1 OUTPUT: 5 6 In addone: num1 = 6 int int In main: num1 = 5 56

57 Good Programming Practice Your header comments should be neatly formatted and contain the following information: function name function description (what it does) a list of any input parameters and their meanings a list of any output parameters and their meanings a description of any special conditions /* maxium compute the max of two integers * Input: two integers * Output: the maximum of the input; * if the input are equivalent, return the 2nd integer */ int maximum (int a, int b) { if (a > b) return a; else return b; } Top-Down Design Complex problems can be solved using top-down design, also known as stepwise refinement, where We break the problem into parts. Then break the parts into parts. Until, each of the parts will be easy to implement the code. 57

58 Top-Down Design with Functions Input Process Output Main Draw Outline Draw Chimney Draw Door Draw Windows Draw Door Frame Draw Knob 1. Assignment 2 2. Assignment 3 1. 年 2. 年 3. leap year 4. 利列數 58

C/C++ - 函数

C/C++ - 函数 C/C++ Table of contents 1. 2. 3. & 4. 5. 1 2 3 # include # define SIZE 50 int main ( void ) { float list [ SIZE ]; readlist (list, SIZE ); sort (list, SIZE ); average (list, SIZE ); bargragh