Learning notes on February 5, 2022 (C language)

22/2/5 Learning notes （Part 1）

main function

1、 A project has and There is only one main function .
2、 There can be more than one project .c file .

data type

• char // Character data type （ Can be a specifier ）
• short // Short
• int // integer —%d
• long // Long integer
• long long // Longer integers
• float // Single-precision floating-point —%f
• double // Double precision floating point —%lf

The scope and life cycle of variables

• The scope of a local variable ： The local scope of the variable .
• Scope of global variables ： The whole project .

   int g_val = 2022

• The life cycle of a variable is the period of time between the creation and destruction of a variable

Constant

• Literal constants
• const Modified constant variable

 const int num = 10; // here num It's a constant （ Properties that cannot be changed ）.

• #define Defined identifier constant

  #define MAX 10000;

• Enumeration constants enum（ Enumeration constants are from... By default 0 Start , Every increase 1. Assignable initial value .）

 enum  Enumerate class names   //（SEX）
 {
    
       type 1  //(MALE)
       type 2  //(FEMALE)
       type 3  //(SECRET)
 };

character string + Escape character + notes

• “abcdef” // character string
• \0 // The string hides a... At the end \0 The logo of （ End mark ）.[ There is no such thing as .]

little tips

• printf(“”); // Print out “”

• print("%d\n", 100)`; // Print out an integer “100”

• sizeof // keyword - The operator - Calculate the space occupied by the type or variable .

• {} Externally defined are global variables , Internally defined are local variables . When local variables and global variables conflict , Local priority .

• scanf("%d %d",&a,%b); // User defined , That is, you need to enter
  

• scanf_s function Do not belong to c Language category . Try not to use . If you don't have to use , You can add... To the first line of the entire source file ：#define_CRT_SECURE_NO_WARNINGS 1【 Use Notepad to open and copy this command in the programming software , The word will appear in the first line of the newly opened programming page .】

• int arr[10] = {0}; // An array of ten numbers

• Debugging is very important .

• extern Statement

• strlen(); //string length Find the length

 int len = strlen("abc");
 printf("%d\n",len);