C 语言学习-06【指针】

1、目标单元与简介存取

直接访问和间接访问

#include <stdio.h>int main(void) {int a = 3, *p;p = &a;printf("a = %d, *p = %d\n", a, *p);*p = 10;printf("a = %d, *p = %d\n", a, *p);printf("Enter a: ");scanf("%d", &a);printf("a = %d, *p = %d\n", a, *p);(*p)++;printf("a = %d, *p = %d\n", a, *p);return 0;
}

• 运行结果：
  

2、引用指针变量

引用指针变量

#include <stdio.h>int main() {int a = 15;int *p = &a;printf("%d, %d\n", a, *p);return 0;
}

• 运行结果：
  

通过指针修改内存上的数据

#include <stdio.h>int main() {int a = 15, b = 99, c = 222;int *p = &a;*p = b;c = *p;printf("%d, %d, %d, %d\n", a, b, c, *p);return 0;
}

• 运行结果：
  

3、指针变量作为函数参数

通过指针交换两个变量的值：

#include <stdio.h>void swap(int *p1, int *p2) {int temp;temp = *p1;*p1 = *p2;*p2 = temp;
}int main() {int a = 66, b = 99;swap(&a, &b);printf("a = %d, b = %d\n", a, b);return 0;
}

• 运行结果：
  

4、指向数组的指针

通过指针输出数组中元素的值

#include <stdio.h>int main(void) {int i, a[] = {1, 3, 5, 7, 9};int *p = a;for (i = 0; i < 5; i++) {printf("%d\t", *(p+i));}printf("\n");return 0;
}

• 运行结果：
  

5、指向数组的指针作为函数参数

利用数组名作为参数，将数组中的 10 个整数完全颠倒顺序：

#include <stdio.h>void inv(int *x, int n);int main() {int i, a[] = {3, 7, 9, 11, 0, 6, 7, 5, 4, 2};printf("The original array: \n");for (i = 0; i < 10; i++) {printf("%3d", a[i]);}printf("\n");inv(a, 10);printf("The array has been inverted: \n");for (i = 0; i < 10; i++) {printf("%3d", a[i]);}printf("\n");return 0;
}void inv(int *x, int n) {int t, *i, *j;for (i = x, j = x + n - 1; i <= j; i++, j--) {t = *i;*i = *j;*j = t;}return;
}

• 运行结果：
  

6、字符串指针

八进制转换成十进制：

#include <stdio.h>int main(void) {char *p, s[6];int n;n = 0;p = s;printf("Enter the octal number you want to convert: \n");gets(p);while (*(p) != '\0') {n = n * 8 + *p - '0';p++;}printf("The converted decimal number is: \n%d\n", n);return 0;
}

• 运行结果：
  

7、指针复制字符串

字符串复制：

#include <stdio.h>int main(void) {char str1[10], str2[10];char *p1, *p2;p1 = str1;p2 = str2;printf("Please enter the original string: \n");gets(p2);for (; *p2 != '\0'; p1++, p2++) {*p1 = *p2;}*p1 = '\0';printf("The original string is %s\n, and the copied string is %s\n", str2, str1);return 0;
}

• 运行结果：
  

字符串连接：

#include <stdio.h>int main(void) {char str1[10], str2[10], str[10];char *p1, *p2, *p;int i = 0;p1 = str1;p2 = str2;p = str;printf("Please enter the str1: \n");gets(p1);printf("Please enter the str2: \n");gets(p2);while (*p1 != '\0') {*p = *p1;p += 1;p1 += 1;i++;}for (; *p2 != '\0'; p1++, p2++, p++) {*p = *p2;}*p = '\0';printf("str1 is %s\nstr2 is %s\nAfter connection is: %s\n", str1, str2, str);return 0;
}

• 运行结果：
  

已知一个字符串，使用返回指针的函数，实现把该字符串中的 ‘*’ 号删除，同时把后面连接的字符串前移

#include <stdio.h>
#include <string.h>char *strarrange(char *arr) {char *p = arr;char *t;while (*p != '\0') {p++;if (*p == '*') {t = p;while (*t != '\0') {*t = *(t + 1);t++;}p--;}}return arr;
}int main(void) {char s[] = "abc*def***ghi*jklmn";char *p;p = s;printf("Before deletion, the character string is: %s\n", p);printf("After deletion, the character string is: %s\n", strarrange(p));return 0;
}

• 运行结果：
  

8、函数指针

指向函数的指针：

#include <stdio.h>int max(int x, int y) {int z;if (x > y) {z = x;} else {z = y;}return z;
}int main(void) {int(*p)(int, int);int a, b, c;p = max;printf("Enter the values of a and b\n");scanf("%d %d", &a, &b);c = (*p)(a, b);printf("The larger value of %d and %d is: %d\n", a, b, c);return 0;
}

• 运行结果：
  

9、使用 const 修饰指针变量

• const 类型 *变量名：可以改变指针的指向，不能改变指针指向的内容
• 类型 * const 变量名：可以改变指针指向的内容，不能改变指针的指向
• const 类型 * const 变量名：指针的指向、指针指向的内容都不可以改变

10、数值排序

实现将 3 个数值进行降序排列：

#include <stdio.h>
#include <stdlib.h>void fun(int *a, int *b) {int temp;temp = *a;*a = *b;*b = temp;
}void exchange(int *a, int *b, int *c) {if (*a < *b) fun(a, b);if (*a < *c) fun(a, c);if (*b < *c) fun(b, c);
}void main() {int *p1 = (int*)malloc(sizeof(int));int *p2 = (int*)malloc(sizeof(int));int *p3 = (int*)malloc(sizeof(int));printf("Please input 3 numbers: \n");scanf("%d %d %d", p1, p2, p3);exchange(p1, p2, p3);printf("Output: \n");printf("*p1 = %d\t*p2 = %d\t*p3 = %d\n", *p1, *p2, *p3);free(p1);free(p2);free(p3);
}

• 运行结果：