Catalog:

• constant
• String+Escape Character+Comment
• Selection Statement
• Loop statement
• array
• Operator

Beginning of text:

Constant:

Constants in C are divided into the following categories:

• Literal Constant
• const-modified constant variable
• Identifier Constant defined by #define
• enumeration constant

int main()
{
  //Literal Constant Demo
  3.14;//Literal Constant
  1000;//Literal Constant
}

int main()
{
  //const-modified constant variable
  const float pai = 3.14;  //pai here is a const-modified constant variable
  pai = 5.14;//It cannot be modified directly!
  printf("%f",pai);
}

(At this point, the output is 3.14, pai is modified by const, and the pai value is unchanged)

pai in the example above is called a const-modified constant variable. Const-modified constant variable is only grammatically restricted in C. The variable pai cannot be changed directly, but pai is essentially a variable, so it is called a constant variable.

int main()
{
  //#define's demonstration of identifier constants
  #define MAX 100
  printf("max = %d\n", MAX);
}

(The output value is: max = 100)

#include <stdio.h>
int main
{
   //Give an example
   enum Sex
   {
     MALE,
     FEMALE,
     SECRET
   };
   //MALE,FEMALE,SECRET in parentheses are enumeration constants
   //Enumeration Constants Demo
   printf("%d\n", MALE);
   printf("%d\n", FEMALE);
   printf("%d\n", SECRET);
   //Note: By default, enumeration constants start at 0 and increment down by 1
}

The default for enumeration constants is to start at 0 and increment down by 1, so the output value is:

0

1

2

Be careful!!!

When defining an array, use the following methods to define that c99, PTA, Niukou Passenger Networks are working properly, and errors may occur in other environments.

Understand this: the first line of code states that n is a variable, in which case n is initialized and given an initial value; Arrays need to be defined with constants, so errors will occur!

Character string:

A string of characters caused by double quotation marks is called a String Literal or simply a string.
Note: The end flag of the string is an escape character of \0. \0 is the end flag when calculating the length of a string and is not counted as the string content.

 

Extend knowledge: the difference between strlen and sizeof (focus!!!)

1.strlen is not necessarily related to sizeof;

2.strlen is for string length, only for string length, is a library function, and needs a header file;

3.sizeof calculates the size of variables, arrays, and types in bytes, which are operators

char arr1[]="abc";
char arr2[]={'a','b','c'};  //Output results:
printf("%d\n",sizeof(arr1));//4A B C \0 (including \0)
printf("%d\n",sizeof(arr2));//3   a b c
printf("%d\n",strlen(arr1));//3A B C \0 (excluding \0)
printf("%d\n",strlen(arr2));//Random value strlen continues to look backwards for'\0'

 

 

Escape characters:

Escape Character Interpretation
\?: Use when writing consecutive question marks to prevent them from being resolved into three-letter words
\': Used to represent character constants'
\": Double quotation marks used to represent the interior of a string
\: Used to represent a backslash to prevent it from being interpreted as an escape sequence character.
\a: warning character, beep
\b: Backspace character
\f: Paper feed note
\n: Line break
\r: Enter
\t: Horizontal tabs
\v: Vertical tab
\ddd:ddd represents one to three octal digits. For example: X
\xdd:dd represents two hexadecimal digits. For example: \x30

/What does the program output?
#include <stdio.h>
int main()
{
  printf("%d\n", strlen("abcdef"));
  // In the following line of code, \t\ is parsed into an escape character//output result: 14 (Error prone!!!)
  printf("%d\n", strlen("c:\test\628\test.c"));
  return 0;
}

Note:

1. Unnecessary code in the code can be deleted or commented out
2. Some of the code is difficult to understand, so add a comment

(When writing code, it's best to comment on it appropriately to make it more readable and convenient for others and yourself! It's also a good code style! I hope your friends will notice this.)

There are two styles of notes:
1.C Language Style Comments /*xxxxx*/
Defect: Comments cannot be nested
2.C++ style comment //xxxxxxx
One or more lines can be commented on

#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++ Comment Style
  //int a = 10;
  //Call the Add function to complete the addition
  printf("%d\n", Add(1, 2));
  return 0;
}

Selection statement:

if statement

switch Statements

#include <stdio.h>
int main()
{
  int coding = 0;
  printf("Will you try to type the code? (Select 1 or 0):>");
  scanf("%d", &coding);
  if(coding == 1)
 {
   prinf("You'll be fine offer\n");
 }
  else
 {
   printf("Eat the bitterness of life\n");
 }
  return 0;

(So, friends choose 1 or 0, haha, I helped you choose 1, duck-feeding!)

 

 

Loop statement:

the while statement
for statement
Do... the while statement

//Instances of a while loop
#include <stdio.h>
int main()
{
  printf("Learning Programming\n");
  int line = 0;
  while(line<=20000)
 {
    line++;
    printf("I want to keep working hard on the code\n");
 }
  if(line>20000)
    printf("good offer\n");
  return 0;
}

Array:

Definition of an array: a collection of elements of the same type

Definition of the array:

int arr[10] = {1,2,3,4,5,6,7,8,9,10};// Define an integer array with up to 10 elements

Subscripts to arrays:

Language C specifies that each element of an array has a subscript, which starts with 0.

Arrays can be accessed through subscripts.

For example:

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

 

Use of arrays:

#include <stdio.h>
int main()
{
  int i = 0;
  int arr[10] = {1,2,3,4,5,6,7,8,9,10};
  for(i=0; i<10; i++)//i starts with 0 because array subscripts start with 0
  {
    printf("%d ", arr[i]);
  }
  printf("\n");//Output result: 1 2 3 4 5 6 7 8 9 10
  return 0;
}

Operator:

arithmetic operator

+  -  *  /  %

Shift operators

>>  << 

Bitwise operators

&  ^  | 

Assignment operator

=  +=  -=  *=  /=  &=  ^=  |=  >>=  <<= 

unary operator

! Logical Inverse Operations
- Negative values
++ Positive Value
& Get Address
The type length (in bytes) of the sizeof operand
~ Bitwise inversion of a number
-- Front and rear--
+++ Front and Back++.
** Indirect access operator (dereference operator)
(Type) Cast type

Relational Operators

>
>=
<
<=
!= Used to test "inequality"
== Used to test equality

Logical Operator

&& Logic and
|| Logical or

Conditional Operator

exp1 ? exp2 : exp3 

Comma expression

exp1, exp2, exp3, ...expN

Subscript references, function calls, and structure members

[] () . -> 

(Get a general overview first, followed by a detailed description in the blog, don't have to memorize by heart, you can gradually remember by reading and writing the code)

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