C language-06 complex data types-03 pointer,-06 data type-03 pointer

C language-06 complex data types-03 pointer,-06 data type-03 pointer
Pointer variable definition

Variable type * variable name;

# Include <stdio. h> int main () {// pointer: You can access the corresponding bucket based on an address value. // int before the pointer Variable p: pointer Variable p can only point to int type data int * p; // defines a pointer Variable p
Int a = 90; p = & a; // the pointer Variable p points to the variable a. the pointer variable can only store addresses.

* P = 10; // * different from * when defining pointer variables, it indicates that the corresponding bucket a = 20 is accessed; printf ("% d \ n ", * p); return 0 ;}

Pointer-related

/* % D int % f float \ double % ld long % lld long % c char % s string % zd unsigned long */# include <stdio. h> int main () {char * cp; int * ap; long * bp; printf ("cp = % zd, ap = % zd, bp = % zd \ n ", sizeof (cp), sizeof (ap), sizeof (bp ));
// Any pointer occupies 8 bytes of storage space 64-bit compiler think about why the pointer should be categorized (the computer determines the number of bytes of content retrieved from the memory based on the pointer type)}

 

Exercise

// Modify the external variable # include <stdio. h> void change (int * p); int main () {int a = 10; change (& a); printf ("a = % d \ n", ); return 0;} void change (int * p) {* p = 20 ;}

 

// Use a pointer to indirectly return multiple values. # include <stdio. h> int main () {int a = 15; int B = 10; int he = 0, cha = 0; test (a, B, & he, & cha ); printf ("and % d, difference is % d", he, cha);} void test (int a, int B, int * c, int * d) {* c = a + B; * d = a-B ;}

Pointer and array

# Include <stdio. h>/* 1. array Element access method int ages [5]; int * p; p = ages; 1> array name [subscript] ages [I] 2> pointer variable name [subscript] p [I] 3> * (p + I) // The pointer's + 1 is not a value plus 2. pointer variable + 1. How much the address value is added depends on the pointer type int * 4 char * 1 double * 8 */void change (int array []); int main () {// 20 bytes int ages [5] = {10, 11, 19, 78, 67}; change (ages); return 0 ;} // use a pointer to receive an array. the pointer variable array points to the first element of the array void change (int * array) {printf ("% d \ n ", array [2]); // printf ("% d \ n", * (array + 2);}/* void change (int array []) {int s = sizeof (array); printf ("% d \ n", s);} */void test () {double d = 10.8; double * dp; dp = & d; printf ("dp = % p \ n", dp); printf ("dp + 1 = % p \ n", dp + 1 ); int ages [5] = {10, 9, 8, 67, 56}; int * p; // The pointer Variable p points to the first element of the array p = & ages [0]; // The array name is the address of the array and the address of the first element of the array // p = ages; /* p ---> & ages [0] p + 1 ---> & ages [1] p + 2 ---> & ages [2] p + I ---> & ages [I] * // printf ("% d \ n ", * (p + 2); printf ("% d \ n", p [2]);/* for (int I = 0; I <5; I ++) {printf ("ages [% d] = % d \ n", I, * (p + I);} * // printf ("% p \ n ", p); // printf ("% p \ n", p + 1); // printf ("% p \ n", p + 2 );}

Pointer and string

# Include <stdio. h>/* 1. the constant area stores some constant strings. heap object 3. stack stores local variables: Two Methods for defining strings 1> using the array char name [] = "itcast"; // string variables * features: the characters in the string can be modified * usage: the content of the string needs to be modified frequently // char name [] = "it"; // name [0] = 'T '; // printf ("% s \ n", name ); // "it" = 'I' + 'T' + '\ 0' 2> using the pointer char * name = "itcast"; // String constant * features: A string is actually a constant string, and the characters in it cannot be modified * usage: the content of the string does not need to be modified, and this string is often used and cached, the newly defined pointer is out of memory space. // char * name2 = "it"; // char * name3 = "it"; // * name2 = 'T '; // The program will crash. It is a constant that cannot be modified // printf ("% c \ n", * name2 ); // The pointer variable name2 points to the string's first character printf ("% p \ n", name2, name3 ); // do not open the new space with the same address // printf ("% s \ n", name2); // until \ 0 */int main () {char name [20] is encountered; printf ("Enter name: \ n"); scanf ("% s", name ); // 'J' 'a 'C' k'' \ 0' // printf ("% c \ n", name [3]); // printf ("the input string is % s \ n", name); return 0 ;}// define the string array void test2 () {char * name = "jack"; // int ages [5]; // pointer array (String Array) char * names [5] = {"jack ", "rose", "jake"}; // two-dimensional character array (String Array) char names2 [2] [10] = {"jack", "rose "};}