1 / 30

Arrays, Pointers, and Strings in C++ Programming

Learn about array usage, pointers, and string processing in C++. Includes examples and details on multi-dimensional arrays, argument passing, and string processing functions.

ethelheller
Download Presentation

Arrays, Pointers, and Strings in C++ Programming

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. C++ Lecture 3 Monday, 14 July 2003

  2. Arrays, Pointers, and Strings • Use of array in C++, multi-dimensional array, array argument passing • Pointers • Relation between pointer and array • String, string processing functions

  3. Arrays • Declaration of an array int c[12]; • or const int max = 12; int c[max]; • References to an array c[ ] c[0], c[1], …, c[max-1]

  4. Array Initialization int n[5] = {1, 2, 3, 4, 5}; • or int n[ ] = {1, ,2, 3, 4, 5}; • n[0], n[1], …, n[4] are valid references C.f. Fig. 4.3

  5. Array of Characters (String) char string1[20]; char string2[ ] = "string literal"; • Individual array element is a character string2[3] = 'y'; C.f. Fig. 4.12

  6. Passing Array • Passing an array name is equivalent to passing the address of the array int a[5]; // declare array func(a); // use function void func(int a[ ]) // define function { } C.f Fig. 4.14

  7. Array Name is a constant Address int a[100]; a is the address of a[0], a+k is the address of a[k]. a–1, or a+100, is also a valid address; C/C++ cannot check array index out of bound error during compile or run time.

  8. Multiple-Subscripted Arrays int a[2][5]; • A 2 by 5 array. • Initialization int a[2][5] = { {0,1,2,3,4}, {0,2,4,6,8} }; • Row major convention in C/C++

  9. Argument Passing for Multi-Dimensional Array int a[3][5]; func(a); • or func(a+1); void func(int b[ ][5]) { ... C.f Fig. 4.22

  10. Pointers • Pointer value holds the address of a variable. • Pointers are also typed, i.e, pointer to int is considered different from pointer to double. • E.g., int *p; double *fpt;

  11. Declaration of Pointer Variables int *p; // a pointer to int int c; // an int variable p = &c; // address of c is given to p • The value of variable p is the address of c. • The value at the address stored in p is the value of c. *p = 2; // dereferencing

  12. Address Operator & int c, *p, a[100]; p = &c; // address of c p = a; // address of array p = &a[0]; // same as above

  13. Dereferencing Operator * int *p, c; c = 1; p = &c; // let p point to c j = *p; // j gets 1,

  14. Operator Precedence and Associativity ( ) [ ] left to right highest ++, --, &, * right to left unary * / % left to right multiply + , - left to right additive <<, >> left to right insertion <, <=, >, >= left to right relational ==, != left to right equality , left to right comma

  15. Left to Right Association • a + b + c means (a+b) + c • Precedence • a + b*c means a + (b*c)

  16. Adding Parentheses ( … ) to show the order of evaluation • b += x = y - k*a[ j ] && 3 | u < v--; • See Appendix A, page 1214 for the complete "Operator Precedence Chart".

  17. Answer b += (x = ((y - (k*(a[ j ]))) && (3 | (u < (v--)))));

  18. Call-by-Reference with Pointer • Passing a pointer can modify the value in calling program. int c; cube_it(&c); void cube_it(int *p) { ... C.f. Fig.5.7

  19. Pointer to const data and const Pointers void f(const int *p); • The data pointed by p cannot be modified. int * const p = &x; // p always // pointing to x const int *const p = &x; // p always // points to x, x cannot change

  20. Relationship between Pointers and Arrays • An expression of *(a + k) • is considered totally equivalent to a[k]. • E.g., a[0] is the same as *a.

  21. Multi-Dimensional Array • In the declaration int a[3][7]; we can view a as pointer to array of a[0], a[1], a[2], which themselves are pointers to int array a[i][j]. • **a is the same as a[0][0].

  22. Pointer of Pointers a a[2][0] a[2][1] a[0] a[1] a[2] a[1][0] a[1][1] ... a[0][0] a[0][1] a[0][2] ...

  23. Arrays of Pointers char *suit[4] = { "Hearts", "Diamonds", "Clubs", "Spade"}; • suit[0][0] refers to 'H', • suit[3][4] refers to 'e' in "Spade", • suit[2][20] is an illegal access.

  24. Function Pointer void (*f)(int); • f is a pointer to a function of the form void g(int). • Function names are like address, e.g, f = g; (*f)(5); // call the function

  25. Fundamentals of Characters and Strings char c, s[10]; // declare variables c = 'a'; // can be used as small int s = "John Q"; // don't work, why? • You must do s[0] = 'J'; s[1] = 'o'; s[2] = 'h'; // etc • Or use string copy function

  26. String Initialization char color[ ] = "blue"; char *colorPtr = "blue"; char color[ ] = {'b', 'l', 'u', 'e', '\0'}; • What is the difference between the array color and the pointer colorPtr?

  27. Read a String char word[20]; cin >> word; // cause problem cin >> setw(20) >> word; // OK • Read an entire line char sentence[80]; cin.getline(sentence, 80);

  28. String Processing Functions <string.h> char *strcpy(char *t, const char *s); char *strncpy(char *t, const char *s, size_t n); char *strcat(char *t, const char *s); int strcmp(const char *s, const char *t); size_t strlen(const char *s);

  29. String Processing • Examples from Fig.5.30 and 5.31. C.f. Fig 5.30 and 5.31

  30. Exercise 4.29 • (The Sieve of Eratosthenes) A prime integer is any integer that is evenly divisible only by itself and 1. Use the sieve method to find prime. • Initialize a[1000] all to 1 (for true). • Starting from 2, 3, …, k, ..., set array indices which are all multiple of k to 0, • print the nonzero indices.

More Related