Learning C Language. For BEGINNERS. Remember! Practice will make you perfect!!! :D. The 6 th week / May 24 th, Su-Jin Oh

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1 Remember! Practice will make you perfect!!! :D Learning C Language For BEGINNERS The 6 th week / May 24 th, 26 Su-Jin Oh sujinohkor@gmail.com 1

2 Index Basics Operator Precedence Table and ASCII Code Table Bit Operators Constant Values Type Casting Functions and Scope Rules Pointers Pointer-1: Pointers Pointer-2: Pointers and Arrays Pointer-3: Pointers and Functions 2

3 Bit Operators, Constant Values, and Type Casting BASICS 3

4 ASCII Code Table IMPORTANT 0 A a ASCII (decimal)

5 Operator Precedence Table Primary Unary Dyadic 5

6 Bit Operators Operator Meaning Cases ~ Bitwise Complement ~0 1 ~1 0 << Bitwise Shift Left >> Bitwise Shift Right & Bitwise AND ^ Bitwise Exclusive OR Bitwise (Inclusive) OR The left operands value is moved left by the number of bits specified by the right operand. The left operands value is moved right by the number of bits specified by the right operand. 0 & & & & ^ ^ ^ ^ &: If both bits are 1, then the result is 1. ^: If both bits are different, then the result is 1. : If the either bit is 1, then the result is 1. 6

7 Constant Values 1/2 Constant - [NOUN] A constant is a thing or value that always stays the same. Literals Integer Literals: Integer numbers. e.g. 0, 11, 0xFF, 20u, 40l, 60ul Floating-point Literals: Real numbers. e.g. 0.1, 3.14, E-5L Character Literals: These are enclosed in single quotes. e.g. a, \n... String Literals: These are enclosed in double quotes. e.g. Hello, Hallym University - 11: octal - 20u: unsigned int - 40l: long - 60ul: unsigned long Defining Constants Using #define Preprocessor Using const Keyword 7

8 Constant Values 2/2 Using #define Preprocessor #include <stdio.h> #define WID 5 #define HEI 10 int area = WID * HEI; printf("width(%d) * height(%d) = area(%d)\n", WID, HEI, area); Using const Keyword #include <stdio.h> const int WID = 5; const int HEI = 10; int area = WID * HEI; printf("width(%d) * height(%d) = area(%d)\n", WID, HEI, area); 8

9 Type Casting Is this really necessary? YES 08 Then, how can we correct the above code? 08 #include <stdio.h> int a = 1, b = 2; float f = a / b; printf("%d / %d = %f\n", a, b, f); #include <stdio.h> int a = 1, b = 2; float f = (float)a / b; printf("%d / %d = %f\n", a, b, f); You may think that the result is 0.5. But!!!!!! The result is 0!!! 9

10 Functions, Call Types, Scope Rules, and Recursion FUNCTIONS AND SCOPE RULES 10

11 Functions #include <stdio.h> int sum(int num1, int num2); int max(int, int); Calling Functions printf(" = %d\n", sum(10, 5) ); printf("10 and 5, the larger one is %d\n", max(10, 5) ); int sum(int num1, int num2) { return num1+num2; int max(int num1, int num2) { int res; if(num1 > num2) res = num1; else res = num2; return res; Function Declarations Both are allowed. Defining Functions return_type function_name(parameter list) { function body

12 Call Types 1/3 Call by Value This method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument. e.g. max(num1, num2); Call by Reference This method copies the address of an argument into the formal parameter. Inside the function, the address is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument. e.g. swap(&x, &y); 12

13 Call Types 2/3; Call by Value #include <stdio.h> void swap(int x, int y); int a = 100, b = 200; printf("before swap, a is %d, b is %d\n", a, b); swap(a, b); printf("after swap, a is %d, b is %d\n", a, b); void swap(int x, int y) { int temp = x; x = y; y = temp; return; The result will be Before swap, a is 100, b is 200 After swap, a is 100, b is

14 Call Types 3/3; Call by Reference #include <stdio.h> void swap(int *x, int *y); int a = 100, b = 200; printf("before swap, a is %d, b is %d\n", a, b); swap(&a, &b); printf("after swap, a is %d, b is %d\n", a, b); void swap(int *x, int *y) { int temp = *x; *x = *y; *y = temp; return; The result will be Before swap, a is 100, b is 200 After swap, a is 200, b is

15 Scope Rules 1/ #include <stdio.h> int a = 100; void globala(); int a = 10; printf("the local variable a is %d\n", a); globala(); void globala() { printf("the global variable a is %d\n", a); Unlike local variables, global variables are automatically initialized by the system. Data Type Default Value The result will be The local variable a is 10 The global variable a is 100 int char float double pointer 0 \0 (NULL) 0 0 NULL 15

16 Scope Rules 2/ #include <stdio.h> void locala(); void statica(); locala(); statica(); locala(); statica(); The result will be The local variable a is 10 The static variable a is 100 The local variable a is 10 The static variable a is 1 void locala() { int a = 10; printf("the local variable a is %d\n", a++); void statica() { static int a = 100; printf("the static variable a is %d\n", a++); 16

17 Recursion #include <stdio.h> int Factorial(int n); int Fibonacci(int n); int i; printf("5! is %d\n", Factorial(5)); printf("fib(5) is [ "); for(i=0; i<=5; i++) printf("%d ", Fibonacci(i)); printf("]\n"); int Factorial(int n) { if(n == 0) return 1; else return n * Factorial(n-1); int Fibonacci(int n) { The result will be 5! is 120 Fib(5) is [ ] if(n < 2) return n; else return Fibonacci(n-1) + Fibonacci(n-2); 17

18 POINTER-1 POINTERS 18

19 Memory Space When we make some variables, then 19 char c = a ; int i = 7; double d = 3.14; 0x1000 c = a 0x10 i = 7 0x10 0x10 0x10 0x10 d=3.14 0x10 0x10 0x1008 0x1009 0x100A 0x100B 0x100C 0x100D 0x100E adding...

20 What are Pointers? When we make a pointer, then int i = 100; int *pi = &i; Below is invalid! int *p = 100; 0x1000 i = 100 0x10 0x10 0x10 0x x2000 0x20 0x20 0x20 0x20 0x100C adding pi = 0x A pointer variable is that stores the memory address of another variable. The size of a pointer variable is fixed regardless of its type. (x86: 4-byte / x64: 8-byte) The type of a pointer indicates the size of the referenced memory space. (If there is no type in pointers, then computers cannot know how many memory spaces they should access.) 20

21 The Operator Sizeof() char c = 'a', *pc = &c; int i = 10, *pi = &i; double d = 3.14, *pd = &d; printf("sizeof(pc):%d\n", sizeof(pc)); printf("sizeof(*pc):%d\n", sizeof(*pc)); printf("sizeof(pi):%d\n", sizeof(pi)); printf("sizeof(*pi):%d\n", sizeof(*pi)); printf("sizeof(pd):%d\n", sizeof(pd)); printf("sizeof(*pd):%d\n", sizeof(*pd)); Can you explain this code? 21

22 * and & Operators Case-1 Case-2 int i = 100; int *pi = &i; int i = 100; int *pi = &i; This instruction makes a pointer variable. The pointer pi points out the variable i s address. The value of the memory which is indicated by the variable pi. The variable pi s address printf( pi:%x / *pi:%d / &pi:%x\n, pi, *pi, &pi); printf( i:%d / &i:%x\n, i, &i); The variable i s address 0x1000 i 0x2000 pi 100 0x

23 What If We Compile Below Codes? Case-1 int i = 100, *pi = &i; printf( *pi:%d\n, *pi); The ++ operator has precedence over the * operator. (*pi)++; printf( *pi:%d\n, *pi); Case-2 23 int n = 100, *p1 = &n, *p2 = p1; printf("%d\n", (*p1)++); printf("%d\n", (*p2)++); printf("%d\n", n); The result will be p1 0x1000 n p x1000 0x1000

24 POINTER-2 POINTERS AND ARRAYS 24

25 Arrays int arr[5] = { 10, 20, 30, 40, 50 ; An array s name means the 1 st element s address of the array x1000 0x10 0x1008 0x100C 0x arr[0] arr[1] arr[2] arr[3] arr[4] int arr[5] = {10,20,30,40,50; printf("arr:%x\n", arr); printf("&arr:%x\n", &arr); printf("&arr[0]:%x\n", &arr[0]); printf("&arr[1]:%x\n", &arr[1]); printf("*arr:%d\n", *arr); printf("*(arr+1):%d\n", *(arr+1)); The result will be

26 A Pointer to an Array Case-1 Case int arr[5] = {10,20,30,40,50; int *p = arr; printf("p[0]:%d, p[1]:%d\n", p[0], p[1]); int arr[5] = {10,20,30,40,50; int *p = arr; printf("%d\n", *p); printf("%d\n", *(++p)); printf("%d\n", *(++p)); printf("%d\n", *(p+1)); printf("%d\n", *(p+2)); The result will be p[0]:10, p[1]:20 The result will be

27 arr[i] is the Same as *(arr+i) int arr[5] = {10, 20, 30, 40, 50; int *p = arr; The result will be arr[0]:10, *(arr+1):20 p[0]:10, *(p+1):20 printf("arr[0]:%d, *(arr+1):%d\n", arr[0], *(arr+1)); printf("p[0]:%d, *(p+1):%d\n", p[0], *(p+1)); Using an Array Using a Pointer arr[0] arr[1] arr[2] arr[3] arr[4] *(arr+0) *(arr+1) *(arr+2) *(arr+3) *(arr+4) p[0] p[1] p[2] p[3] p[4] *(p+0) *(p+1) *(p+2) *(p+3) *(p+4) 27

28 Practices Practice-1 Practice int arr[5] = {10,20,30,40,50; int *p = arr; The result will be arr[0]:10, *(arr+1):20 p[0]:10, *(p+1):20 printf("p[0]:%d, p[1]:%d\n", p[0], p[1]); int arr[5] = {10, 20, 30, 40, 50; int *p = arr, i, temp; for(i = 0; i <4-i; i++) { temp = p[i]; p[i] = p[4-i]; p[4-i] = temp; The result will be for(i = 0; i < 5; i++) p[0]:50 p[1]:40 p[2]:30 p[3]:20 p[4]:10 printf("p[%d]:%d\t", i, p[i]); printf("\n"); 28

29 Pointers and Strings Both are similar. However, actually they are different!!! 1. char str1[6] = hello ; 2. char *str2 = HELLO ; 1. A String Variable h e l l o \0 str1[0] str1[1] str1[2] str1[3] str1[4] str1[5] str1[1] = a ; str2[1] = A ; // ERROR!!! Why the 2 nd statement makes an error? 2. A Pointer Variable 0x2000 str2 Try it!!! Both are the same! 0x2000 HELLO\0 printf("str1:%s\n", str1); printf("str2:%s\n", str2); printf( str2:%x\n, str2); printf("&str2:%x\n", &str2); printf("&(*str2):%x\n", &(*str2)); 29

30 A String Constant char *str = HELLO ; 0x2000 str 0x2000 HELLO\0 What if we initialize two pointer variables as the same string? 0x2000 str1 0x2000 str2 0x2000 HELLO\0 These are the same! printf("str1:%x\n", str1); printf("str2:%x\n", str2); printf("*str1:%c\n", *str1); printf("*str2:%c\n", *str2); printf("*(str1+1):%c\n", *(str1+1)); printf("*(str2+1):%c\n", *(str2+1)); printf("&str1:%x\n", &str1); printf("&str2:%x\n", &str2); printf("&(*str1):%x\n", &(*str1)); printf("&(*str2):%x\n", &(*str2)); 30

31 An Array of Pointers Case-1 Case int a = 10, b = 20; int *arr[2] = {&a, &b; printf("*arr[0]:%d\n", *arr[0]); printf("*arr[1]:%d\n", *arr[1]); char *p[2] = { "Hallym University, Korea", "Su-Jin Oh" ; printf("p[0]:%s\n", p[0]); printf("*(p+1):%s\n", *(p+1)); printf("*p[0]:%c\n", *p[0]); printf("*(p[0]+1):%c\n", *(p[0]+1)); The result will be *arr[0]:10 *arr[1]:20 The result will be p[0]:hallym University, Korea *(p+1):su-jin Oh *p[0]:h *(p[0]+1):a 31

32 POINTER-3 POINTERS AND FUNCTIONS 32

33 Passing Pointers/Arrays to Functions #include <stdio.h> void mul(int *arr, int len); void div(int arr[], int len); int arr[] = {10, 20, 30; mul(arr, sizeof(arr)/sizeof(arr[0])); printf("after mul: %d %d %d\n", arr[0], arr[1], arr[2]); div(arr, sizeof(arr)/sizeof(arr[0])); printf("after div: %d %d %d\n", arr[0], arr[1], arr[2]); void mul(int *arr, int len) { int i; for(i = 0; i < len; i++) arr[i] *= 10; void div(int arr[], int len) { int i; for(i = 0; i < len; i++) arr[i] /= 10; If you want to fix the length of this array, then you can write like int arr[10]. The operator sizeof() - When you use it to an array, then you can get the whole size of the array. - When you use it to a pointer variable, then you will get the size of a pointer variable. (x86: 4-byte / x64: 8-byte) When you declare a function s arguments, both int arr[] and int *arr are the same.

34 Return an Array from a Function #include <stdio.h> #define NUM 10 int *setvalues(void); int i, *p = setvalues(); printf("*(p + i): "); for(i = 0; i < NUM; i++) printf("%d ", *(p+i)); printf("\n"); To return the address of a function's local variable is not allowed in C. int *setvalues() { Thus, you need to define the key word static. int i; static int values[num]; printf("values[i]: "); for(i = 0; i < NUM; i++) { values[i] = i*10; printf("%d ", values[i]); printf("\n"); return values; If you delete this word, then the compiler may report a warning. warning: function returns address of local variable

35 Const Case-1 Case-2 Case-3 35 int a = 10; const int *p = &a; //*p = 30; // Error!!! a = 30; printf("*p:%d\n", *p); int a = 10, b = 30; int *const p = &a; //p = &b; // Error!!! *p = 30; printf("*p:%d\n", *p); int a = 10, b = 30; const int *const p = &a; //p = &b; // Error!!! //*p = 30; // Error!!! printf("*p:%d\n", *p); The variable a cannot be changed through the pointer variable p. The pointer variable p cannot point out another variable. The pointer variable p cannot point out another variable, further the variable a cannot be changed through the pointer variable p.

36 Thanks for attending :D THE END 36

To declare an array in C, a programmer specifies the type of the elements and the number of elements required by an array as follows

To declare an array in C, a programmer specifies the type of the elements and the number of elements required by an array as follows Unti 4: C Arrays Arrays a kind of data structure that can store a fixed-size sequential collection of elements of the same type An array is used to store a collection of data, but it is often more useful