C language - first program, print, variables and constants

Catalog

One 、C Characteristics of language ：

Two 、 The first program

3、 ... and 、 Escape character

Four 、 Variables and constants

1. Variable

 2. Constant

3. Define symbolic constants

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One 、C Characteristics of language ：

High flexibility 、 Efficient 、 High portability

Two 、 The first program

1. Software ：Dev-C++ 5.11

2. step ：

        file → newly build → Source code

        function → Compile operation →( Save type )C source files(*.c)→（ file name ）test.c→ preservation

#include <stdio.h>

int main()
{
	printf("Hello World\n");
	return 0;
	
}

3. Code run results

3、 ... and 、 Escape character

Escape character	meaning
\a	Ring the bell （BEL）
\b	Backspace （BS）, Move the current position to the previous column
\f	Change the page （FF）, Move the current position to the beginning of the next page
\n	Line break （LF）, Moves the current position to the beginning of the next line
\r	enter （CR）, Move the current position to the beginning of the line
\t	Horizontal TAB （HT）, Skip to the next TAB Location
\v	Vertical tabulation （VT）
\\	Indicates that the backslash itself （\）
\'	For single quotes （’）
\"	Double quotation marks （"）
\?	Indicates a question mark （？）
\0	For empty characters （NULL）
\ddd	1 To 3 Any character represented by an octal number
\xhh	1 To 2 Any character represented by hexadecimal digits

Four 、 Variables and constants

        Variables and constants are two basic data objects processed by programs .

1. Variable

（1） The meaning of variable is to determine the target and provide storage space .

（2） Variable name ： Variable names can only be in English letters （A-Z,a-z） And number （0-9） Or underline （_） form .

          Naming rules ：① The first letter must start with a letter or an underline ;

                           ② Variable names are case sensitive ;

                                eg:_FISHC ≠ fishc

                           ③ You cannot use keywords to name variables .

（3） keyword

auto	break	case	char	const	continue	default	do
double	else	enum	extern	float	for	goto	if
int	long	register	return	short	signed	sizeof	static
struct	switch	typedef	union	unsigned	void	volatile	while

inline

restrict

_Bool

_Complex

_Imaginary

_Alignas

_Alignof

_Atomic

_Static_assert

_Noreturn

_Thread_local

_Generic

（4） data type

• char — Character , Take up one byte
• int — integer , It usually reflects the most natural length of an integer in the machine used
• float — Single precision floating point
• double — Double precision floating point

eg:int a;char b;float c;double d

（5） Code ：

#include <stdio.h>

int main()
{
	int a;
	char b;
	float c;
	double d;
	
	a = 520;
	b = 'F';
	c = 3.14;
	d = 3.141592653;
	
	printf(" fish C The studio was founded in 2010 Year of %d\n",a);
	printf("I love %cishC.com!\n",b);
	printf(" PI is ：%.2f\n",c);
	printf(" Accurate to the decimal point 9 The Pi of bit is ：%11.9f\n",d);
	
	return 0;
	
}

Running results ：

 2. Constant

• integer constants ：520,1314,123
• Real constant ：3.14,5.12,8.97
• character constants ： Ordinary character ：'L','O','V','E'; Escape character ：'\b','\t','\n'
• String constant ：“FishC”
• Symbolic constant ： You must define before using

3. Define symbolic constants

（1） Format ：#define identifier Constant

        such as ：- #define URL"http://www.fishc.com"
                   - #define NAME" fish C Studio ”
                   - #define BoSS“ Little turtle ”
                   - #define YEAR 2010
                   - #define MONTH5
                   - #define DAY 20

Code ：

#include <stdio.h>

#define URL "http://www.fishc.com"
#define NAME " fish C Studio "
#define BOSS " Little turtle "
#define YEAR 2010
#define MONTH 5
#define DAY 20

int main()
{
	printf("%s Founded on %d year %d month %d Japan \n",NAME,YEAR,MONTH,DAY);
	printf("%s yes %s Created ……\n",NAME,BOSS);
	printf("%s The domain name of is %s\n",NAME,URL);
	
	return 0;
}

Running results ：

（2） identifier （identifier）

• Identifiers can only be English letters （A-Z,a-z） And number （0-9） Or underline （_） form （eg：_ i_love_fishC_520）
• The first letter must start with a letter or an underline
• Identifiers are case sensitive （eg:_ FISHC ≠ fishc）
• You cannot use keywords to name identifiers

（3） String constant

• character ：'F','I','S','H','C'

'F'

'I'

'S'

'H'

'C'

• character string ：

——"Hello World"

'H'

'e'

'l'

'l'

'o'

' '

'W'

'o'

'r'

'l'

'd'

'\0'

——"I love FishC.com!"

'I'	' '	'l'	'o'	'v'	'e'	' '	'F'	'i'
's'	'h'	'C'	'.'	'c'	'o'	'm'	'!'	'\0'