[C language] shallow selection, circular statements, functions and arrays

Catalog

choice 、 Loop statement  

Sequential structure

  Selection structure （ Conditional control statements ）

  Loop structure

  function

Array

To define an array

The array subscript

choice 、 Loop statement  

C Language is 【 structured 】 The programming language of , Contains three structures

• Sequential structure
• Selection structure
• Loop structure

  Everything we experience in life can be expressed in three structures .

Sequential structure

The sequential structure is the structure executed from front to back in the order of writing . This kind of structure is the simplest , It is also the most basic structure . Generally, written programs basically use sequential structure .

  Selection structure （ Conditional control statements ）

• if sentence
• if···else sentence
• Conditional expression （C The only ternary operator in language ）
• switch sentence

Take a small example , This article is just a little understanding , The specific content will be explained in detail in the following article .

int main()
{
   printf(" Went to University \n");
   printf(" Should you study hard \n");
   scanf("%d", &input);
   if input ==1
   {
      printf(" Find a good job \n");
   }
   else
   {
      printf(" Can't find a good job \n");
   }

   return 0;
}

  Loop structure

• for sentence
• while sentence
• do···while sentence  

  Next use while Statement introduces a simple example , Details later articles will explain in detail .

int main()
{
   int money = 0;
   printf(" start-up \n");
  
   while(money < 20000)
   {
      printf(" To work hard \n");
      money++;
   }
   if(money >= 20000)
   {
      printf(" happy life \n");
   }
   else
   {
      printf(" Make persistent efforts \n");
   }


   return 0;
}

  function

function A unit of independent program code that performs a specific task . Function can save us the task of writing code repeatedly , If the program needs to perform a task multiple times , Then we just need to write a suitable function , Just call it whenever you need it . It also makes the program we write more modular , It is convenient for later revision and improvement .

Take a simple example to roughly understand the function .

If we want the sum of two integers , We'll do that .

int main()
{
   int n1 = 0;
   int n2 = 0;
   
   // Input 
   scanf("%d %d", &n1, &n2);
   
   // Sum up 
   int sum = n1 + n2;
   
   // Print 
   printf("%d\n", sum);


   return 0;
}

  Next, we write a function in advance to calculate the addition of two integers , Then call it when you need to calculate .

int Add(int x, int y)//Add Is the function name , In parentheses are function parameters ,int Is the return type 
{
   int z = 0;
   z = x + y;
   return z;
}
// Function body in curly brackets 


int main()
{
   int n1 = 0;
   int n2 = 0;
   
   // Input 
   scanf("%d %d", &n1, &n2);

   // Sum up 
   int sum = Add(n1, n2);
   
   // Print 
   printf("%d", sum);


   return 0;
}

Array

To define an array

Array Is a collection of elements of the same type .

We need to write a program , It is inevitable to deal with a large amount of data , Arrays can process these data efficiently and conveniently .

int arr[10] = {0,1,2,3,4,5,6,7,8,9};

The array subscript

C Language policy , Each element of an array has a subscript , The subscript is from 0 At the beginning .

Arrays can be accessed through subscripts .

int arr[10] = {0};
// If the array has 10 Elements , So the subscript range is 0~9

int main()
{
   int arr[10] = {1,2,3,4,5,6,7,8,9};
   printf("%d\n", arr[8]);
   // The printout is 9

   return 0;
}

Of course, it is also possible to print the elements in the array one by one .

#include<stdio.h>
int main()
{
	int arr[10] = { 1,2,3,4,5,6,7,8,9 };
	int i = 0;
	while (i < 9)
	{
		printf("%d", arr[i]);
		i++;
	}

	return 0;
}

We can also create different types of arrays .

int main()
{
   int arr[];
   char ch[];
   double[];

   return 0;
}

int main()
{
   char arr[4] = {'b','i','t'};
   // This is incomplete initialization , The remaining parts are initialized as 0

   return 0;
}

//C99 Before standard , The size of arrays is specified by constants or constant expressions 
int arr1[10] = {0};
int arr2[6+4] = {0};
//C99 After standard , Variable length arrays are supported , At this time, the array size is allowed to be a variable 
// But the array specified in this way cannot be initialized 
int m = 100;
int arr3[m];
// The compiler I use VS Yes C99 The syntax support in is not very good , Variable length arrays are not supported .