[C Language] Summary of array knowledge (2) - Input and output of strings

1. Storage of strings

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• The stored string must have the end mark '\0'

• The length of the array storing the string is at least the effective length of the string + 1

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Read the code below carefully to understand:

#include<stdio.h>
int main()
{
    
    
    char str1[6] = {
    
     'c', 'h', 'i', 'n', 'a' };
    printf("%c\n", str1[5]);  // 输出空字符
    printf("%d\n", str1[5] == '\0');  // 判断是否含有空字符

    char str2[5] = {
    
     'c', 'h', 'i', 'n', 'a' };
    printf("%c\n", str2[5]);  // 错误输出
    printf("%d\n", str2[5] == '\0');  // 判断是否含有空字符

    char str3[6] = {
    
     'c', 'h', 'i', 'n', 'a', '\0' };
    printf("%c\n", str3[5]);  // 输出空字符
    printf("%d\n", str3[5] == '\0');  // 判断是否含有空字符

    char str4[6] = {
    
     "china" };
    printf("%c\n", str4[5]);  // 输出空字符
    printf("%d\n", str4[5] == '\0');  // 判断是否含有空字符

    char str5[5] = {
    
     "china" };
    printf("%c\n", str5[5]);  // 错误输出
    printf("%d\n", str5[5] == '\0');  // 判断是否含有空字符

    char str6[6] = "china";
    printf("%c\n", str6[5]);  // 输出空字符
    printf("%d\n", str6[5] == '\0');  // 判断是否含有空字符

    return 0;
}

Output result:

According to the output result:

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• 1 3 4 6 is equivalent and correct
• 2 5 is wrong

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2. String input and output

1. Comparison of several input and output strings

function	Format	the difference
scanf()	scanf("%s", character array name)	You cannot enter a string with spaces. You can use multiple format control characters %s to enter multiple strings. When a space is encountered to end the input, you need to add the end of string mark '\0' manually.
gets()	get(character array name)	Only one string can be entered. The input ends when a carriage return character is encountered, and the carriage return character '\n' is automatically converted to '\0'
printf()	printf("%s", character array name)	A printf() function can output multiple strings without automatically wrapping lines after output.
puts()	puts(character array name)	A puts() function can only output a string, and it will automatically wrap after output.

2. Character-by-character input and output

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• Use the standard input and output functions scanf() and printf() with the %c format descriptor
• A fixed number of characters must be entered

---

#include<stdio.h>
int main()
{
    
    
	int i; 
	char str[11];
	printf("请输入十个字符:");
	for (i = 0; i < 10; i++)
		scanf("%c", &str[i]);
	str[i] = '\0';
	i = 0;
	while (str[i] != '\0')
	{
    
    
		printf("%c", str[i]);
		i++;
	}
	return 0;
}

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• Use the getchar() and putchar() functions to input and output strings
• Just enter the number of characters within the specified limit and end when you enter the carriage return character.

---

#include<stdio.h>
int main()
{
    
    
	int i=0; 
	char str[80];
	printf("请输入一串字符:");
	while ((str[i] = getchar()) != '\n')
		i++;
	str[i] = '\0';
	for (i = 0; str[i] != '\0'; i++)
		printf("%c", str[i]);
	return 0;
}

3. Overall input of string

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• Use the standard input function scanf() with the %s format descriptor
• Calling format: scanf("%s", character array name);
• When using the %s format control character to input a string, the scanf() function will automatically add '\0' after the string.

---

#include<stdio.h>
int main()
{
    
    
	char str[10];
	printf("请输入一串字符：");
	scanf("%s", str);//不用& str就是地址
	printf("%s\n", str);
	return 0;
}

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When you need to input a string containing spaces in the middle, you need to use the scanf() function with multiple input parameters to match the input.

---

#include<stdio.h>
int main()
{
    
    
	char str1[5],str2[5], str3[5];
	scanf("%s%s%s", str1, str2, str3);
	printf("%s %s %s\n", str1, str2, str3);
	return 0;
}

result:

how are you
how are you

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• Use the function gets() to enter a complete string
• Calling format: gets(character array name);
• This function can store a line of characters entered by the keyboard into a character array in the form of a string.
• When entering a line of characters, the Enter key is used as the end character, and the carriage return character '\n' is automatically converted to '\0' as the end mark of the string.

---

#include<stdio.h>
int main()
{
    
    
	char str[50];
	gets(str);
	printf("%s\n", str);
	return 0;
}

result:

how are you
how are you

4. String output

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• Use the standard output function printf() with the %s format descriptor
• Calling format: printf("%s", character array name);

---

#include<stdio.h>
int main()
{
    
    
	char str1[]="How are you?";
	char str2[] = "I am fine.Thank you.";
	printf("%s\n%s\n", str1,str2);
	return 0;
}

result:

How are you?
I am fine.Thank you.

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• Use the function puts() to output a complete string
• Calling format: puts(character array name);
• This function can output a string (a sequence of characters ending with '\0') to the screen
• Will automatically wrap after output

---

#include<stdio.h>
int main()
{
    
    
	char str[]="How are you?";
	puts(str);
	printf("I am fine.Thank you.");
	return 0;
}

result:

How are you?
I am fine.Thank you.//可看出换了行