C语言基础学习——第4天(数组)
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00array_define.c
#include <stdio.h>int main(void){ // 数组和指针都是复合类型, 它们从另外一种基础类型(基本类型, 结构类型)派生. // 定义数组时, // 1. 确定数组元素的类型. // 2. 显式或隐式的确定数组的元素个数. // 这里的 '[]' 是声明说明符号. int ary[5]; int a[] = { 36, 48, 12, 6, -3 }; int i = 0; printf("sizeof ary = %u, sizeof ary[0] = %u\n", sizeof(ary), sizeof(ary[0])); printf("sizeof ary / sizeof ary[0] = %u\n", sizeof(ary) / sizeof(ary[0])); printf("----------------------------------\n"); // 这里的 '[]' 是运算符, 索引访问运算符号. for (i = 0; i < 5; i++) printf("a[%d] = %d\n", i, a[i]); // 越界 越界产生不确定的运行行为. // a[5] = 4; return 0;}运行结果:sizeof ary = 20, sizeof ary[0] = 4sizeof ary / sizeof ary[0] = 5----------------------------------a[0] = 36a[1] = 48a[2] = 12a[3] = 6a[4] = -301array_name.c
#include <stdio.h>int main(void){ int a[5] = { 36, 48, 12, 18, }; int b[5]; // 数组名代表数组首元素地址. 数组名是一个常量值. // b = a; // 非法. printf("a = %p, &a[0] = %p\n", a, &a[0]); printf("a = %p, &a[1] = %p\n", a, &a[1]); return 0;}运行结果:a = 0xbfaea908, &a[0] = 0xbfaea908a = 0xbfaea908, &a[1] = 0xbfaea90c02array_arg.c
#include <stdio.h>// 当数组作为函数参数时, 退化为一个指针.// 即当作为函数参数时, 如下形参等价.// --> int a[10] == int a[] == int *avoid test(int a[10]){ printf("in test, sizeof a = %u\n", sizeof(a));}void rand_a(int a[], int len){ int i = 0; for (i = 0; i < len; i++) a[i] = rand() % 100;}void print_a(int *a, int len){ int i = 0; for (i = 0; i < len; i++) printf("%d ", a[i]); putchar('\n');}int main(void){ int a[10] = {0}; printf("in main, sizeof a = %u\n", sizeof(a)); printf("---------------------\n"); test(a); printf("=====================\n"); rand_a(a, sizeof(a) / sizeof(a[0])); print_a(a, sizeof(a) / sizeof(a[0])); return 0;}运行结果:in main, sizeof a = 40---------------------in test, sizeof a = 4=====================83 86 77 15 93 35 86 92 49 2103c99_define.c
#include <stdio.h>int main(void){ // C99 int a[] = { [0] = 32, [3] = 45, [4] = 16 }; int i = 0; for (i = 0; i < sizeof(a) / sizeof(a[0]); i++) printf("a[%d] = %d\n", i, a[i]); return 0;}运行结果:a[0] = 32a[1] = 0a[2] = 0a[3] = 45a[4] = 1604array_operation.c
#include <stdio.h>void rand_a(int a[], int len){ int i = 0; for (i = 0; i < len; i++) a[i] = rand() % 100;}void print_a(int a[], int len){ int i = 0; for (i = 0; i < len; i++) printf("%d ", a[i]); putchar('\n');}int max(int a[], int len){ int i = 0, max = a[0]; for (i = 0; i < len; i++) { if (a[i] > max) max = a[i]; } return max;}int min(int a[], int len){ int i = 0, min = a[0]; for (i = 0; i < len; i++) { if (a[i] < min) min = a[i]; } return min;}void reverse(int a[], int len){ int i = 0; for (i = 0; i < len / 2; i++) { a[i] ^= a[len-i-1]; a[len-i-1] ^= a[i]; a[i] ^= a[len-i-1]; }}void bubble_sort(int a[], int len){ int i = 0, j = 0; for (i = 0; i < len - 1; i++) { for (j = 0; j < len - i - 1; j++) { if (a[j] > a[j+1]) { a[j] ^= a[j+1]; a[j+1] ^= a[j]; a[j] ^= a[j+1]; } } }}int main(void){ int a[10] = {0}; rand_a(a, 10); print_a(a, 10); printf("--------------------\n"); printf("max = %d\n", max(a, 10)); printf("min = %d\n", min(a, 10)); printf("--------------------\n"); printf("reverse:\n"); reverse(a, 10); print_a(a, 10); printf("--------------------\n"); printf("sort:\n"); bubble_sort(a, 10); print_a(a, 10); return 0;}运行结果:83 86 77 15 93 35 86 92 49 21--------------------max = 93min = 15--------------------reverse:21 49 92 86 35 93 15 77 86 83--------------------sort:15 21 35 49 77 83 86 86 92 9305char_array.c
#include <stdio.h>#include <string.h>int main(void){ // char str[] = {'c', 'h', 'i', 'n', 'a', ' ', 'u', 'n', 'i', 'x', '\0' }; char str[] = "china unix"; // 在内存中, 默认字符串以 '\0' 结束. 即 '\0' 是字符串结束的标志. // '\0' 结尾字符 NUL字符 空字符 ascii编码为 0 // '0' 0字符 ascii编码为 48 // sizeof 是一个运算符, 它在编译期求值(数组的元素个数). printf("sizeof str = %u\n", sizeof(str)); // strlen 是库函数, 它在运行期求值(不包含'\0'的字符个数). printf("length of str = %u\n", strlen(str)); printf("------------------------\n"); printf("sizeof \"china unix\" = %u\n", sizeof "china unix"); // 要用 \ 来显示双引号 printf("length of \"china unix\" = %u\n", strlen("china unix")); printf("========================\n"); // s 空间放不下 '\0', 错误. char s[10] = "china unix"; // s1 空间足够放下字符串. 没有赋 '\0'. // 给了数组初始化式后, 未初始化的部分自动赋0(就是'\0') // 如下初始化式是正确的. char s1[10] = { 'C', 'H', 'I', 'N', 'A' }; printf("s[10] = %s\n", s); // 会把s1也给打印出来, 因为s1在栈中是放在了s之后的, 且s1有尾零 return 0;}运行结果:sizeof str = 11length of str = 10------------------------sizeof "china unix" = 11length of "china unix" = 10========================s[10] = china unixCHINA06out_of_range.c
#include <stdio.h>int main(void){ int b = 25; int a[5] = { 1, 2, 3, 4, 10 }; int i = 0; // 屏蔽与不屏蔽的运行结果不一样 printf("&b = %p\n", &b); printf("a = %p\n", a); printf("&i = %p\n", &i); // i == 5 时越界了. for (i = 0; i < 6; i++) printf("a[%d] = %d\n", i, a[i]); a[5] = 36; // 越界 // 这是一种巧合. printf("b = %d\n", b); return 0;}运行结果(屏蔽掉3句打印地址值的printf):a[0] = 1a[1] = 2a[2] = 3a[3] = 4a[4] = 10a[5] = 5 --> 随机值b = 25运行结果(不屏蔽3句打印地址值的printf):&b = 0xbfe0aca8a = 0xbfe0ac94&i = 0xbfe0acaca[0] = 1a[1] = 2a[2] = 3a[3] = 4a[4] = 10a[5] = 25 --> b的值b = 36 --> b被修改了07infinite_loop.c
#include <stdio.h>int main(void){ int a[5] = { 12, 34, 56, 78, 90 }; int i = 0; printf("a = %p\n", a); printf("&i = %p\n", &i); // 越界访问导致无限循环(这是一种巧合). for (i = 0; i < 5; i++) { printf("%d\n", a[i]); a[5] = 2; // 越界, 相当于 i = 2; sleep(1); } return 0;}运行结果:a = 0xbf9eeef8&i = 0xbf9eef0c127878787878...08puts.c
#include <stdio.h>int main(void){ char s1[10] = "helloworld"; // 没有尾零 char s2[] = "HELLO"; // 有尾零 // 输出到 '\0' 停止, 自动加换行. 等价于 printf("%s\n", s1); puts(s1); printf("--------------\n"); puts(s2); return 0;}运行结果:helloworldHELLO--------------HELLO09gets.c
#include <stdio.h>int main(void){ char s[1024] = {0}; printf("pls input a string: "); gets(s); // scanf("%s", s); printf("-----------\n"); printf("you inputed: "); puts(s); // printf("%s\n", s); return 0;}10my_atoi.c
#include <stdio.h>int judge_format(char s[]){ int i = 0; while (s[i] != '\0') { if (!('0' <= s[i] && s[i] <= '9')) break; i++; } if (s[i] == '\0') // 表示已到尽头 return 1; else return 0;}unsigned int my_atoi(char s[]){ int i = 0; unsigned int n = 0; while (s[i] != '\0') { n *= 10; n += s[i++] - '0'; } return n;}int main(void){ char s[128] = {0}; unsigned int a = 0;retry: printf("pls input a string: "); gets(s); if (judge_format(s)) { a = my_atoi(s); printf("a = %u\n", a); } else { printf("pls input a integer.\n"); goto retry; } return 0;}exercise1.c
#include <stdio.h>#include <string.h>int insert_char(char s[], int len, int index, char ch)// 指定下标插入{ int i = 0, s_len = strlen(s); if((s_len + 1) >= len) // 包括将要插入的字符在内, 是否大于等于len, 等于的话, 尾零就放不下了 { printf("input string too long!\n"); return -1; } if(index < 0 || index > s_len) { printf("input wrong index!\n"); return -1; } i = s_len; while(i >= index) { s[i+1] = s[i]; // 往后挪一位 i--; } s[index] = ch; return 0;}int main(void){ char s[128] = {0}; char ch = '0'; int index = 0, ret = 0; printf("input a string: "); gets(s);retry: printf("input a index to insert your char: "); ret = scanf("%d", &index); // 清空输入缓冲区. while(getchar() != '\n') ; if(ret == 0) { printf("input wrong format, pls input again.\n"); goto retry; } printf("input the character you wanna insert: "); ch = getchar(); if(0 == insert_char(s, sizeof(s)/sizeof(s[0]), index, ch)) { printf("insert succeed!\n"); puts(s); } else { printf("insert failed!\n"); } return 0;}往字符串中插入字符运行结果:input a string: abcdefghjiklmninput a index to insert your char: 5input the character you wanna insert: Winsert succeed!abcdeWfghjiklmnexercise2.c
#include <stdio.h>int my_strlen(const char src[]) // 获取字符串长度{ int len = 0; while(src[len++] != '\0') ; return len - 1;}void my_strcpy(char dest[], const char src[]) // 拷贝字符串{ int i = 0; while(src[i] != '\0') { dest[i] = src[i]; i++; } dest[i] = '\0'; // 最后别忘了再赋一个尾零}void my_strcat(char dest[], const char src[]) // 在一个字符串的结尾追加另一个字符串{ int d_len = my_strlen(dest); my_strcpy(dest + d_len, src); // dest 先偏移 d_len 个单位, 再传给 my_strcpy}int my_strcmp(const char s1[], const char s2[]) // 比较两个字符串{ int i = 0; while((s1[i] != '\0') && (s2[i] != '\0')) { if(s1[i] != s2[i]) break; i++; } return (s1[i] - s2[i]);}char *my_strchr(char *src, int ch) // 在src中查找第一次c出现的位置, 并返回该位置的指针{ int i = 0; while(src[i] != '\0') { if(src[i] == ch) return (src+i); i++; } return NULL;}char *my_strstr(char parent[], char child[]) // 在parent中查找第一次child出现的位置, 并返回该位置的指针{ int i = 0, j = 0, start_pos = 0; for(i = 0; parent[i] != '\0'; i++) { if(parent[i] == child[0]) // 和 child 的首字符相等了再进来继续判断 { start_pos = i; for(j = 1; child[j] != '\0'; j++) // j 从 1 开始 { if(parent[++start_pos] != child[j]) break; } if(child[j] == '\0') return (parent+i); // i 保存的就是起始位置 } } return NULL;}int main(void){ char dest[1024] = {0}, src[1024] = {0}; int ret = 0; char *str = NULL; printf("please input a string: "); gets(src); printf("len = %d\n", my_strlen(src)); printf("------------------\n"); printf("src = %s\n", src); my_strcpy(dest, src); printf("dest = %s\n", dest); printf("------------------\n"); my_strcat(dest, src); printf("dest = %s\n", dest); printf("------------------\n"); ret = my_strcmp(dest, src); if(ret == 0) printf("dest == src\n"); if(ret > 0) printf("dest > src\n"); if(ret < 0) printf("dest < src\n"); printf("------------------\n"); str = my_strchr(dest, '5'); printf("str = %s\n", str); printf("------------------\n"); str = my_strstr(dest, "abcd"); printf("str = %s\n", str); return 0;}实现 my_strlen, my_strcpy, my_strcat, my_strcmp, my_strchr, my_strstr运行结果:please input a string: 0123456789abcdelen = 15------------------src = 0123456789abcdedest = 0123456789abcde------------------dest = 0123456789abcde0123456789abcde------------------dest > src------------------str = 56789abcde0123456789abcde------------------str = abcde0123456789abcdeexercise3.c
#include <stdio.h>#include <string.h>void reverse(char s[], int len){ int i; for (i = 0; i < len/2; i++) { s[i] ^= s[len-i-1]; s[len-i-1] ^= s[i]; s[i] ^= s[len-i-1]; }}void add(char s1[], char s2[], char sum[]){ int len1 = strlen(s1); int len2 = strlen(s2); int len_max = len1 > len2 ? len1 : len2; // 为了更方便的运用数组操作, 需要倒置一下字符串 reverse(s1, len1); reverse(s2, len2); int i = 0, digit = 0, carry = 0; for (i = 0, digit = 0; i < len_max; i++, digit = 0) { if (s1[i] != '\0') digit += s1[i] - '0'; if (s2[i] != '\0') digit += s2[i] - '0'; digit += sum[i]; // 加上前一次可能的进位. sum[i] = digit % 10; carry = digit / 10; if (carry != 0) sum[i + 1] = carry; sum[i] += '0'; // 转成字符 } if (sum[i] != 0) sum[i] += '0'; reverse(sum, strlen(sum)); // 最后再逆转回来 reverse(s1, len1); reverse(s2, len2);}int main(void){ char s1[128] = {0}, s2[128] = {0}, sum[128] = {0}; printf("input s1: "); gets(s1); printf("input s2: "); gets(s2); add(s1, s2, sum); printf("%s + %s = %s\n", s1, s2, sum); return 0;}字符串加法, 如: "123" + "999" = "1122"实现大数据的相加.运行结果:input s1: 658495129756984566587566458input s2: 498956238486532169463235544658495129756984566587566458 + 498956238486532169463235544 = 1157451368243516736050802002 0 0
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