Chapter 8. Arrays, Addresses, and Pointers : Structured Programming Structured Programming 1

Size: px

Start display at page:

Download "Chapter 8. Arrays, Addresses, and Pointers : Structured Programming Structured Programming 1"

Donna Boyd
6 years ago
Views:

1 Chapter 8 Arrays, Addresses, and Pointers : Structured Programming Structured Programming 1

2 Pointer Pointer is a variable that contains an address. If num_ptr is a pointer, *num_ptr means the variable whose address is stored in num_ptr Structured Programming 2

3 Pointer II int num = 3; int *num_ptr = NULL; (num_ptr is a pointer) num_ptr num NULL 3 num_ptr num num_ptr = &num; 3 num_ptr num num = 5; Structured Programming 3

4 Pointer III num_ptr num *num_ptr = 7; 7 int x = *num_ptr; x num_ptr num Structured Programming 4

5 Pointer IV int *y_ptr = num_ptr; x num_ptr num 7 7 y_ptr Structured Programming 5

6 Pointer V *y_ptr = 6; x num_ptr num 7 6 y_ptr Structured Programming 6

7 Example of Using Pointer I #include<stdio.h> void main() int *ptr; int x = 5; ptr = &x; printf("%d", *ptr); Structured Programming 7

8 Example of Using Pointer II #include <stdio.h> int main() int *numaddr; /* declare a pointer to an int */ int miles,dist; /* declare two integer variables */ dist = 158; /* store the number 158 into dist */ miles = 22; /* store the number 22 into miles */ numaddr = &miles; /* store the 'address of miles' in numaddr */ printf("the address stored in numaddr is %p\n",numaddr); printf("the value pointed to by numaddr is %d\n\n",*numaddr); numaddr = &dist; /* now store the address of dist in numaddr */ printf("the address now stored in numaddr is %p\n",numaddr); printf("the value now pointed to by numaddr is %d\n",*numaddr); return 0; Structured Programming 8

9 Exchange Values #include<stdio.h> void swap(int *x, int *y); void main() int x, y; x = 5; y = 10; swap(&x, &y); printf("x= %d y = %d\n", x, y); void swap(int *x, int *y) int temp; temp = *x; *x = *y; *y = temp; Structured Programming 9

10 Exchange Values (Incorrect) #include<stdio.h> void swap(int x, int y); void main() int x, y; x = 5; y = 10; swap(x, y); printf("x= %d y = %d\n", x, y); void swap(int x, int y) int temp; temp = x; x = y; y = temp; Structured Programming 10

11 1D Array Array is a consecutive series of variables that share one variable name. Declaring an array int grades[5]; //integer uses 2 bytes grades array grades[0] grades[1] grades[2] grades[3] grades[4] Structured Programming 11

12 Example of Using an Array #include <stdio.h> int main() int i; int grades[] = 98, 87, 92, 79, 85; for (i = 0; i <= 4; ++i) printf("\nelement %d is %d", i, grades[i]); return 0; The output produced by the program Element 0 is 98 Element 1 is 87 Element 2 is 92 Element 3 is 79 Element 4 is Structured Programming 12

13 Example of Using an Array II #include <stdio.h> int main() int i, grades[5]; for (i = 0; i <= 4; ++i) /* Enter five grades */ printf("enter a grade: "); scanf("%d", &grades[i]); printf("\n"); for (i = 0; i <= 4; ++i) /* Print five grades */ printf("grades %d is %d\n", i, grades[i]); return 0; Structured Programming 13

14 Output Enter a grade: 85 Enter a grade: 90 Enter a grade: 78 Enter a grade: 75 Enter a grade: 92 grades 0 is 85 grades 1 is 90 grades 2 is 78 grades 3 is 75 grades 4 is Structured Programming 14

15 Array Named as Pointers Now, let us store the address of array element 0 in a pointer. Then, using the indirection operator, *, we can use the address in the pointer to access each array element. For example, if we store the address of grade[0] into a pointer named gptr (using the assignment statement gptr = &grade[0];), then, the expression *gptr, which means the variable pointed to by gptr, references grades[0] Structured Programming 15

16 Array Named as Pointers (Cont.) gptr = &grade[0]; Structured Programming 16

17 Offset Offset may be included in expressions using pointers *(gptr + 1) means grades[1]. *(gptr + 2) means grades[2]. *(gptr + 3) means grades[3]. *(gptr + 4) means grades[4] Structured Programming 17

18 Offset (Cont.) Structured Programming 18

19 Relationship between Array Elements and Pointers Structured Programming 19

20 Array Elements may be Accessed in Two Ways Structured Programming 20

21 Access Array Elements by a Pointer #include <stdio.h> int main() int *gptr; /* declare a pointer to an int */ int i; int grades[] = 98, 87, 92, 79, 85; gptr = &grades[0]; /* store the starting array address */ for (i = 0; i <= 4; ++i) printf("\nelement %d is %d", i, *(gptr + i) ); return 0; The output produced by the program Element 0 is 98 Element 1 is 87 Element 2 is 92 Element 3 is 79 Element 4 is Structured Programming 21

22 Chapter 9 Character Strings : Structured Programming Structured Programming 22

23 String A sequence of characters or an array of characters A string is stored as an array of characters terminated with \0. The figure shows how the string Good Morning! is stored in memory Structured Programming 23

24 gets() and puts() gets() function accepts and stores the characters typed. puts() function displays a string on the screen Structured Programming 24

$h> int main() char message[81]; /* enough storage for a complete line */ printf("enter a string:\n"); gets(message); printf("the$

25 Example of using gets() and puts() #include <stdio.h> int main() char message[81]; /* enough storage for a complete line */ printf("enter a string:\n"); gets(message); printf("the string just entered is:\n"); puts(message); return 0; Structured Programming 25

26 Count Vowels #include<stdio.h> void main() char str[81]; int i=0; int count_a, count_e, count_i, count_o, count_u; count_a = count_e = count_i = count_o = count_u = 0; gets(str); while(str[i]!= '\0') if((str[i] == 'A') (str[i] == 'a')) count_a++; if((str[i] == 'E') (str[i] == 'e')) count_e++; if((str[i] == 'I') (str[i] == 'i')) count_i++; if((str[i] == 'O') (str[i] == 'o')) count_o++; if((str[i] == 'U') (str[i] == 'u')) count_u++; i++; Structured Programming 26

27 printf("the number of a(a) is %d\n", count_a); printf("the number of e(e) is %d\n", count_e); printf("the number of i(i) is %d\n", count_i); printf("the number of o(o) is %d\n", count_o); printf("the number of u(u) is %d\n", count_u); Structured Programming 27

28 strcopy() (Built-in function is strcpy()) #include <stdio.h> void strcopy(char [], char []); /* expects two arrays of chars */ int main() char message[81]; /* enough storage for a complete line */ char newmessage[81]; /* enough storage for a copy of message */ printf("enter a sentence: "); gets(message); strcopy(newmessage, message); /* pass two array addresses */ puts(newmessage); return 0; Structured Programming 28

29 /* copy string2 to string 1 */ void strcopy (char string1[], char string2[]) /* two arrays are passed */ int i = 0; /* i will be used as a subscript */ Output while ( string2[i]!= '\0') /* check for the end-of-string */ string1[i] = string2[i]; /* copy the element to string1 */ ++i; string1[i] = '\0'; /* terminate the first string */ return; Structured Programming 29

$Character-by-Character Input #include <stdio.h> int main() char message[81],c; /* enough storage for a complete line */ int i; printf("enter a string:\n"); Receive a character from a keyboard.$

30 Character-by-Character Input #include <stdio.h> int main() char message[81],c; /* enough storage for a complete line */ int i; printf("enter a string:\n"); Receive a character from a keyboard. i = 0; while( i < 80 && (c = getchar())!= '\n') message[i] = c; /* store the character entered */ ++i; message[i] = '\0'; /* terminate the string */ printf("the string just entered is:\n"); puts(message); return 0; Structured Programming 30

31 Reverse a String #include <stdio.h> #define MAXCHARS 81 void reverse(char [], char []); // Function Prototype int main() char forward[maxchars], rever[maxchars]; printf("enter a line of text: \n"); gets(forward); reverse(forward, rever); // Use the Function printf("\nthe text: %s", forward); printf("\nspelled backwards is: %s", rever); return 0; Structured Programming 31

$= '\0') // count the elements in the string ++i; for(i--;i>=0;j++, i--) rev[j] = forw[i]; rev[j] = '\0';$

32 Output void reverse(char forw[], char rev[]) int i = 0, j = 0; while(forw[i]!= '\0') // count the elements in the string ++i; for(i--;i>=0;j++, i--) rev[j] = forw[i]; rev[j] = '\0'; return; Structured Programming 32

33 String & Function #include <stdio.h> void getline(char []); /* function prototype */ int main () char message[81]; /* enough storage for a complete line */ printf("enter a string: \n"); getline(message); printf("the string just entered is:\n"); puts(message); return 0; Structured Programming 33

34 void getline(char strng[]) int i = 0; char c; while( i < 80 && (c = getchar())!= '\n') strng[i] = c; /* store the character entered */ ++i; strng[i] = '\0'; /* terminate the string */ return; Structured Programming 34

35 String & Pointer #include <stdio.h> int main() char *message2 = "this is a string"; printf("\nthe string is: %s", message2); printf("\n The first address of this string is %p", message2); message2 = "A new message"; printf("\nthe string is now: %s", message2); printf("\n The first address of this string is %p", message2); return 0; Structured Programming 35

36 String & Pointer (Cont.) Structured Programming 36

37 String and Character Library Functions and Routines Structured Programming 37

38 String & ASCII Codes Structured Programming 38

39 Changing a Lowercase Letter to a Uppercase Letter char toupper(char letter) Some ASCII codes if(letter >= 'a' && letter <= 'z') else return (letter - 'a' + 'A'); return (letter); Structured Programming 39

printf("this program adds the value 10 to a given integer number.\n\n");

$printf(this program adds the value 10 to a given integer number.\n\n);$ PA1 Sample Solution Program 1 void add10(int *n); //Prototype int n; printf("this program adds the value 10 to a given integer number.\n\n"); printf("please enter an integer number: "); scanf("%d", &n);