First acquaintance with C language (Part 1)

Here I will give you a brief introduction C Language what we need to learn , Let's have a preliminary understanding .
C Language is a structured programming language , What is structured , That is to say ： Sequential structure , Selection structure , Loop structure , Everything in life is the combination, nesting and repetition of these structures . therefore C Language can solve problems in life through programming .
The development of programming language ： Machine language is binary – Assembly language people program better through some mnemonics –B Language –C Language , At this time C Language is already a high-level language .
C In language, we need to understand

1. Variable
2. Constant
3. data type
4. The scope and life cycle of variables
5. Comment and escape characters
6. keyword
7. Array
8. function
9. The pointer
10. Selection structure
11. Loop structure
12. Structure

Variables and constants

Look at the following code

//1. Literal constants 
//2.const Modified constant variable 
//3. adopt define Defined constant 
//4. Enumeration defined constants 
enum Color
{
    
	Red=0,
	Green=0,
	Blue=0,
};
#define Max 100 
int main()
{
    
	//30;
	//3.14;
	//'W';// character 
	//"abc";
	 stay C In language ,const Embellished a, It's essentially a variable , But it can't be modified directly , There are properties of constants 
	//const int a = 10;
	//a = 20;
	//printf("%d ", a);

	//const int n = 10;
	//int arr[n] = { 0 };// At this time, the error is that the expression must contain a constant value 
	//return 0;
	//Max = 10;// When you want to modify define When defining variable values , You're going to report a mistake .
	//printf("%d\n", Max);
	//Red = 10; // You can see that there will be define The same mistake 
	printf("%d\n", Red);
	return 0;
}

int main()
{
    
	int a = 10;
	a = 20;
	printf("%d\n", a);
	// This is the variable that can be changed 
	return 0;
}

data type

// What are the data types 
// character 
// integer   Short   integer   Long integer   Longer integer 
// floating-point   Single precision floating point   Double precision floating point 
int main(){
    

	printf("%d\n", sizeof(char));//  byte  --1
	printf("%d\n", sizeof(short));// --2
	printf("%d\n", sizeof(int));// --4
	printf("%d\n", sizeof(long));// --4
	printf("%d\n", sizeof(long long));// --8
	printf("%d\n", sizeof(float));// --4
	printf("%d\n", sizeof(double));// --8

	return 0;
}

The life cycle and scope of variables

// Scope of variable 
//1. local variable 
// From the function that created it to the end of this function 
//2. Global variables 
// The scope of global variables is the whole project 

// Life cycle of variable 
// local variable ： Enter the scope and start , Out of scope end 
// Global variables ： The whole life cycle of the program 

int main(){
    

	int a = 10;
	{
    
		//int a = 10;
		printf("%d\n", a);
	}
	printf("%d", a);
	return 0;
}

Comment and escape characters

/* /* int main() {  This is a C The annotation style of language  */
	return 0;
}*/
//int main()
//{
    
//  This is a C++ The annotation style of 
// return 0;
//}

// current C Language has also introduced  // This style 

/**/C This annotation style of language
shortcoming ： You can't nest
C++ The annotation style of
advantage ： Convenient single line notes , You can also comment multiple lines

Escape characters, you can search the Internet to understand it by yourself. There is no more introduction here , But leave a question for everyone , See if you can do it right

int main()
{
    
	// What will the compiler output 
	printf("%s\n","C:\\test\test.c");
	printf("%d\n", sizeof("C:\\test\test.c\x069"));
	return 0;
}

Array

int main()
{
    
	int arr[10] = {
     0 };
	// int  Represents the array type  arr Represents the array name  
	//10-- Array size  {0}--- All ten elements in the array are assigned zero 
	return 0;
}

function

// Write a sum of two numbers 
int ADD(int x, int y)
{
    
	//int  The return type of the function 
	//ADD  Function name 
	//int x,int y  The parameters of the function 
	//{
    
	// return x + y;  These three lines are the function body 
	//}
	return x + y;
}
int main(){
    

	// establish 
	int num1 = 0;// Variable initialization 
	int num2 = 0;

	// Input 
	scanf("%d %d", &num1, &num2);

	// Sum up 
	//int sum = num1 + num2;
	int sum = ADD(num1, num2);

	// Output 
	printf("%d", sum);
	return 0;
}

To be continued …