First knowledge of C language (2)

 

 

Hello everyone , I first met Yu Dong ！

List of articles

• Preface
• 5、 ... and 、 character string + Escape character
• 6、 ... and 、 notes
• 7、 ... and 、 Choose the characters
• 8、 ... and 、 Loop statement
• Nine 、 function
• summary

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Preface

Then the content of the last time , I will continue to share with you the initial stage C language knowledge ！

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5、 ... and 、 character string + Escape character + notes

•   character string

"hello bit.\n"

  This is made up of double quotation marks （Double Quote） The resulting string of characters is called string literal （String Literal）, Or string for short .

notes ： The end flag of the string is '\0' The escape character of . When calculating the length of a string '\0' It's the end sign , It doesn't count as string content .

#include<stdio.h>
#include<string.h>
int main()
{
   char arr1[]="bit";
   char arr2[]={'b','i','t'};
   char arr3[]={'b','i','t','\0'};
   printf("%s\n",arr1);           // The result is 'bit'.
   printf("%s\n",arr2);           // The print result is a pile of garbled .
   printf("%s\n",arr3);           // The result is 'bit'.
   printf("%d\n",strlen(arr1));   // The result is 3.
   return 0;
}

 strlen（string lenth）——> Add #include<string.h>

 strlen It's a library function , Is a function that specifically calculates the length of a string （ Count '\0' The number of characters before ）

• Escape character

example ：

#include<stdio.h>
int main()
{
	printf("c:\code\test.c\n");
	return  0;
}

  This shows the '\t' and '\n' Not printed out ！ I have to mention the escape character here . Escape characters, as the name suggests, change meaning .

Escape character	paraphrase
\?	Use... When writing multiple question marks , Prevent them from being parsed into three letter words
\'	Used to represent character constants '
\"	Double quotation marks used to represent the inside of a string
\\	Used to indicate a backslash , Prevent it from being interpreted as a human escape sequence character .
\a	Warning characters , Beep
\b	Back space
\f	Paper in
\n	Line break
\r	enter
\t	Horizontal tabs
\v	Vertical tabs
\ddd	ddd Express 1-3 Eight octal numbers . Such as \130   (X)
\xdd	dd Express 2 Hexadecimal numbers .      Such as \x30 0

#include<stdio.h>
int main()
{
     printf("%c\n",''\');  // Printed as  '
     printf("%s\n","\"");  // Printed as  "
     return 0;
}

#include<stdio.h>
int main()
{
    printf("%d\n",strlen("abcdef"));       // The result is 6
    printf("%d\n",strlen("c:\test\628\test.c");    // \62 Parsed into an escape character 
    retrurn 0;
}

#include<stdio.h>
int main()
{
printf("%c\n",'\130');   // Printed as X
return 0;
}

  Why does this output X Well ？ Because the octal 130 Convert to decimal to 88,88 Corresponding ASCII In the table X.

 

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  6、 ... and 、 notes

Why do you need comments in your code ？

1. There are unnecessary codes in the code that can be deleted directly , You can also comment out .
2. Some of the code is hard to understand , You can add a comment file .

There are two styles of annotation ：

• C Notes on language style （ You can't nest comments ）
• C++ Notes on language style （ You can comment on a line , You can also comment on multiple lines ）

Code demonstration ：

#include<stdio.h>
int Add(int x, int y)
{
	return x + y;
}
/*C Language style notes 
int Sub(int x, int y)
{
	return x + y;
}
*/
int main()
{
	//C++ The annotation style of 
	//int a=0;
	// call Add function , Complete the addition 
	printf("%d\n", Add(1, 2));
	return 0;
}

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  7、 ... and 、 Select statement

adopt if else Statement to realize the selection of conditions

Code demonstration ：

#include<stdio.h>
int main()
{
	int input = 0;
	printf(" Should you study hard ？（1/0）");
	scanf("%d", &input);
	if (input = 1)
	{
		printf(" good offer\n");
	}
	else
	{
		printf(" Go home and plant \n");
	}
	return 0;
}

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  8、 ... and 、 Loop statement

C How to implement loops in languages ？

• while sentence
• for Loop statement （ Explain in detail later ）
• do ......while sentence （ Explain in detail later ）

Code demonstration while sentence ：

#include<stdio.h>
int main()
{
	printf(" Crazy code writing \n");
	int line = 0;
	while (line <= 20000)
	{
		line++;
		printf(" I'm going to keep typing \n");
	}
	if (line > 20000)
		printf(" The keyboard is broken , Twenty thousand a month \n");
	return 0;
}

  Brothers, the keyboard is broken , Twenty thousand a month ！ No fear of hardship , Work hard ！

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Nine 、 function

Function is characterized by simplifying code , Code reuse

Code demonstration ：

#include<stdio.h>
int main()
{
	int num1 = 0;
	int num2 = 0;
	int num3 = 0;
	printf(" Enter two operands ：");
	scanf_s("%d %d", &num1, &num2);
	num3 = num1 + num2;
	printf("%d", &num3);
	return 0;
}

This code is a little verbose , We can simplify the code through functions ！ 

Simplified code demonstration ：

#include<stdio.h>
int Add(int x, int y)
{
	return x + y;
}
int main()
{
	int a = 0;
	int b = 0;
	printf(" Enter two operands ：");
	scanf_s("%d %d", &a, &b);
	printf("%d",Add(a,b));
	return 0;
}

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summary

The above is the initial stage I summarized for you C Language dry goods , If there are mistakes, welcome baozi to criticize and correct in the comment area ！ I also hope the knowledge I summarized can bring you harvest ！