04-Arrays and strings

overview

All members of the same array are of the same data type, and the addresses of all members in memory are continuous.

one-dimensional array

If the global array is not initialized, the compiler will initialize it to zero. If the local array is not initialized, its content is random.

	int a[10] = {
    
     1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };//定义一个数组，同时初始化所有成员变量
	int a[10] = {
    
     1, 2, 3 };//初始化前三个成员，后面所有元素都设置为0
	int a[10] = {
    
     0 };//所有的成员都设置为0
	
	//[]中不定义元素个数，定义时必须初始化
	int a[] = {
    
     1, 2, 3, 4, 5 };//定义了一个数组，有5个成员

The array name is an address constant, representing the address of the first element in the array.

#include<stdio.h>

int main() {
    
    
	int a[10] = {
    
    1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
	printf("数组名a所表示的地址常量：%p\n", a);
	printf("数组首个元素a[0]的内存地址:%p\n", &a[0]);

	printf("数组a在内存中占%d个字节\n", sizeof(a));
	printf("数组a的元素在内存中占%d个字节\n", sizeof(a[0]));

	printf("开始输出数组a的全部元素：\n");
	for (int i = 0; i < sizeof(a)/sizeof(a[0]); i++) {
    
    
		printf("a[%d]=%d\n", i, a[i]);
	}
	return 0;
}

Run the above code, the output is as follows:

Two-dimensional array

There is no two-dimensional array in the memory. The actual hardware memory of the two-dimensional array is addressed continuously. Storage is the same.

#include<stdio.h>

int main() {
    
    

	//连续赋值
	int a[3][4] = {
    
    1, 2, 3, 4, 5};

	//分段赋值
	//int a[3][4] = { {1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12} };

	for (int i = 0; i < 3; i++) {
    
    
		for (int j = 0; j < 4; j++) {
    
    
			printf("a[%d][%d]=%d\n", i, j, a[i][j]);
		}
	}
}

Execute the above code, the output is as follows:

The array name is a constant address, representing the address of the first element in the array.

#include<stdio.h>

int main() {
    
    
	int a[3][4] = {
    
     {
    
    1, 2, 3, 4}, {
    
    5, 6, 7, 8}, {
    
    9, 10, 11, 12} };

	printf("二维数组名a所代表的地址常量：%p\n", a);
	//第0个一维数组的数组名为a[0]
	printf("二维数组的首个元素a[0]所代表的地址常量：%p\n", a[0]);
	printf("a[0][0]在内存中的地址为:%p\n", &a[0][0]);

	printf("二维数组a在内存中占%d个字节\n", sizeof(a));
	printf("二维数组中的一行在内存中占%d个字节\n", sizeof(a[0]));
	printf("二维数组中的元素在内存中占%d个字节\n", sizeof(a[0][0]));

	printf("二维数组a的行数：%d\n", sizeof(a)/sizeof(a[0]));
	printf("二维数组a的列数：%d\n", sizeof(a[0])/sizeof(a[0][0]));
	printf("二维数组a的行数*列数：%d\n", sizeof(a)/sizeof(a[0][0]));

	//[]中不定义元素个数，定义时必须初始化
	int b[][4] = {
    
    1, 2, 3, 4, 5};
	printf("二维数组b的行数：%d\n", sizeof(b)/sizeof(b[0]));

	return 0;
}

Running the above code, the output is as follows:

Character arrays and strings

The difference between character arrays and strings

• There is no data type of string in C language, which can be replaced by an array of char;
• A string must be an array of char, but an array of char is not necessarily a string;
• A char array ending with the number 0 (equivalent to the character '\0') is a string , but if the char array does not end with the number 0, then it is not a string, just an array of ordinary characters, so the string is a special array of char ;

#include<stdio.h>

int main() {
    
    
	//没有'\0'作为结束符，所以hello1不是字符串，只是普通的字符数组
	char hello1[] = {
    
    'h', 'e', 'l', 'l', 'o'};//末尾输出乱码
	printf("hello1 = %s\n", hello1);
	//hello2以'\0'作为结束符，所以hello2是字符串
	char hello2[] = {
    
     'h', 'e', 'l', 'l', 'o', '\0'};
	printf("hello2 = %s\n", hello2);
	//以第1个'\0'作为结束符，所以不会输出后面的world
	char hello3[] = {
    
     'h', 'e', 'l', 'l', 'o', '\0', 'w', 'o', 'r', 'l', 'd', '\0'};
	printf("hello3 = %s\n", hello3);
	return 0;
}

string initialization

#include<stdio.h>

int main() {
    
    
	char buf[] = {
    
    'I', ' ', 's', 'a', 'y', ':', '\0'};
	//编译器在末尾自动补上\0，所以数组长度为13
	char buf2[] = {
    
    "Hello world!"};
	printf("数组buf2的长度为：%u\n", sizeof(buf2) / sizeof(char));
	//指定长度，后面没有赋值的元素，自动补0
	char buf3[30] = {
    
    "Welcome to"};
	printf("数组buf3的长度为%u\n", sizeof(buf3) / sizeof(char));
	//直接使用字符串初始化，编译器自动在后面补0，常用
	char buf4[] = "our world";
	printf("数组buf4的长度为%u\n", sizeof(buf4) / sizeof(char));


	printf("%s%s\n", buf, buf2);
	printf("C：%s %s!!\n", buf3, buf4);

	//char buf5[2] = { '1', '2', '3' };//数组越界

	char buf5[] = {
    
    'a', 'b', 'c', 0, 'd'};
	char buf6[] = {
    
    'a', 'b', 'c', '0', 'd'};
	char buf7[] = {
    
    'a', 'b', 'c', '\0', 'd'};
	
	printf("输出buf5：%s\n", buf5);
	printf("输出buf6：%s\n", buf6);
	printf("输出buf7：%s\n", buf7);

	//'\0'后面最好不要连着数字，有可能几个数字连起来刚好是一个转义字符
	//'\ddd'八进制字义字符，'\xhh'十六进制转移字符
	// \012相当于\n
	char str[] = "\012abc";
	printf("str == %s\n", str);

	return 0;
}

Running the above code, the output is as follows:

String input and output

gets()

#include <stdio.h>
char *gets(char *s);
功能：从标准输入读入字符，并保存到s指定的内存空间，直到出现换行符或读到文件结尾为止。
参数：
	s：字符串首地址
返回值：
	成功：读入的字符串
	失败：NULL

gets(str)The difference with scanf("%s",str):

• gets(str)The input string is allowed to contain spaces
• scanf("%s",str)no spaces allowed

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>

int main() {
    
    

	char str[100];
	printf("请输入一个字符串（gets）：\n");
	gets(str);
	printf("您输入的是%s\n", str);

	char str2[100];
	printf("请输入一个字符串（scanf）:\n");
	scanf("%s", str2);
	printf("您输入的是%s\n", str2);
	return 0;
}

Running the above code, the output is as follows:

fgets()

#include <stdio.h>
char *fgets(char *s, int size, FILE *stream);
功能：从stream指定的文件内读入字符，保存到s所指定的内存空间，直到出现换行字符、读到文件结尾或是已读了size - 1个字符为止，最后会自动加上字符 '\0' 作为字符串结束。
参数：
	s：字符串
	size：指定最大读取字符串的长度（size - 1）
	stream：文件指针，如果读键盘输入的字符串，固定写为stdin
返回值：
	成功：成功读取的字符串
	读到文件尾或出错： NULL

fgets()When reading a character string entered by the user through the keyboard, the carriage return entered by the user is also regarded as part of the character string. When entering a string through scanfand gets, the ending "\n" is not included, but there are more "\n" at the end through fgets. The fgets() function is safe and there is no buffer overflow problem.

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>

int main() {
    
    
	char str[5];
	
	fgets(str, sizeof(str)/sizeof(char), stdin);
	printf("您输入的是%s\n", str);
	return 0;
}

To run the above code, execute as follows:

puts()

#include <stdio.h>
int puts(const char *s);
功能：标准设备输出s字符串，在输出完成后自动输出一个'\n'。
参数：
	s：字符串首地址
返回值：
	成功：非负数
	失败：-1

fputs()

#include <stdio.h>
int fputs(const char * str, FILE * stream);
功能：将str所指定的字符串写入到stream指定的文件中， 字符串结束符 '\0'  不写入文件。 
参数：
	str：字符串
	stream：文件指针，如果把字符串输出到屏幕，固定写为stdout
返回值：
	成功：0
	失败：-1

fputs()Yes puts()the file manipulation version, but fputs() doesn't automatically output a '\n'.

strlen()

#include <string.h>
size_t strlen(const char *s);
功能：计算指定指定字符串s的长度，不包含字符串结束符‘\0’
参数：
s：字符串首地址
返回值：字符串s的长度，size_t为unsigned int类型

#include<stdio.h>
#include<string.h>

int main() {
    
    
	char str[] = {
    
    'a', 'b', 'c', '\0', 'd'};
	printf("字符串的长度为%u", strlen(str));
	return 0;
}

Run the above code, the execution result is as follows: