Written earlier: This is a floating shadow of C. Can help you quickly browse C's outline~
Catalog
🍕 const-modified constant variable
🍕# Identifier constant defined by define
🍕 Pritf-related issues in strings
🍕 strlen-related problems in strings
🍕 String length including escape characters
Case 1: Logical Inverse Operation
Case 3: ~ Operator action (for positive numbers)
Case 4: ~ Operator action (for negative numbers)
🍕 Conditional operator (trinomial operator) exp1? Exp2: EXP3
🍕 Subscript Reference Operator[]
🍔 constant
🍕 Literal Constant
/ is a value that can be expressed as a string. It includes integer constants, character constants, and string constants.
Note: There are no literal constants of structs such as array constants, struct constants, etc.
#include <stdio.h>
int main()
{
int num=4;
printf("%d\n",num);
num=8;
printf("%d\n",num);//num variable, so you can change
3;
100;
3.14;//Literal Constant
'a';
"abc";
return 0；
}🍕 const-modified constant variable
L: How can I prove that a const-modified constant is a variable?
🐉: Array to prove:
.arr[n] n should be a constant, otherwise errors will occur in VS, because arr[m] in the following program also errors, indicating that const-modified constant M is a variable!
#include<stdio.h>
int main()
{
int n=10;
const int m=10;
int arr[10]={0};
int arr[n]={0};//Error, constants should be placed at n
int arr[m]={0};//error,m is a variable but has a constant attribute, so we say m is a constant variable
//In C99, variable-length arrays are supported, allowing variable classes to specify the size of the array
return 0;
}🍕# Identifier constant defined by define
#include<stdio.h>
#define MAX 10
//Conventional define definitions are typically capitalized
int main()
{
int arr[MAX]={0};
printf("%d\n",MAX);
return 0;
}
🍕 enumeration constant
/ Citation:
//Enumeration=One-to-One Enumeration
//Gender: male, female, confidential
//Three primary colors: red, yellow, blue
//Week: 1,2,3,4,5,6,7
//Enumeration keywords: enum
#include<stdio.h>
enum Sex
{//Enumerate possible values of this type
male,
female,
secret
};
int main()
{
enum Sex s= female;
printf("male=%d\n",male);
printf("female=%d\n",female);
printf("secret=%d\n",secret);
return 0;
}
Case:
1. Variables defined by enumeration constants can be changed
2. Enumeration constants themselves cannot be changed
#include <stdio.h>
enum Color
{
RED,
YELLOW,
BLUE
};
int main()
{
enum Color color =BLUE;
printf("color=%d\n",color);
color=YELLOW;//Variables defined by enumeration constants can be changed
BLUE=6;//The error enumeration constant itself cannot be changed
printf("color=%d\n",color);
return 0;
}
✨✨✨ I am a dividing line ✨✨✨
🍔 Character string
🐉: Let me give you an overview of the first slightly interesting thing - string
. This string of characters caused by double Quotes is called a String Literal or simply a string.
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.
#include <stdio.h>
int main()
{
"abcdefg"//Character string
'a';//character
"a";//Character string
"hello";
"";//Empty String
char arr1[]="abc";//array
char arr2[]={'a','b','c'};
printf("%s\n",arr1);//%s Print String
printf("%s\n",arr2);
return 0 ;
}
L: Why is it so hot when printing arr2?
🐉: Because the end flag of the string is'\0'.
L: What does this have to do with the end sign?
🐉: See the following analysis:
🍕 Pritf-related issues in strings
🍕 strlen-related problems in strings
string length--A function that calculates the length of a string
🐉: When strlen calculates the length of a string\0 is the end flag and does not count as the string content
🐉: For arr1 here, since arr1 is a string and it comes with a hidden'\0', the strlen number stops at c
🐉: For arr2, strlen counts backwards and looks for'\0'until it finds'\0' in the random value, stopping
L: So 218 here is a random value. Maybe it will change after the next recompile?
🐉: Yes!
L: So how can we improve arr2? Let him calculate normally
🐉: Improvements are as follows
#include <stdio.h>
int main()
{
char arr1[]="abc";
char arr2[]={'a','b','c'，'\0'};// Here'\0'can also be replaced by 0 because the value of \0 is 0
//stelen only requires length before'\0'
printf("%d\n",strlen(arr1));
printf("%d\n",strlen(arr2));
return 0 ;
}
. As we can see from the above two tests, adding'\0'and 0 at the end of the arr2 array will calculate the character length normally
This is because the value of'\0'is 0
🍔 Escape Character
The escape character, as its name implies, changes meaning
Case 1: What if you want to type a single quotation mark, a double quotation mark, two consecutive question marks?
Case 2: \ddd and love hatred between decimal and ASCII
\ddd( octal)->corresponding 10-digit number->ASCII character corresponding to decimal number
· Case 3: \xdd and love hatred between decimal and ASCII
\xdd( hexadecimal)->corresponding to decimal number->corresponding ASCII characters for decimal number
🍕 String length including escape characters
🐉: The answer is 14. Is that correct?
L: A piece of cake - guess what? I'll analyze it for you:
✨✨✨ I am a dividing line ✨✨✨
🍔 Notes
✨✨✨ I am a dividing line ✨✨✨
🍔 Selection statement if
Case 1.
Case 2.
. ⚠️ == is equal to / is an assignment within the if statement ()
int main()
{
int a=0;
a=20;//assignment
if(a=30) //The original meaning might be if a equals 30 to output I love you
{
printf("i love u\n"); //Because if statement (a=30) is an assignment statement; A is 3030 is true; must output
}
if(a==40)//Here is a== (equal to) 40, with a assigned to 30 in the if statement above
{
printf(" i hate u\n"); //No Output
}
if(a==30)
{
printf(" i miss u\n"); //Assign a to 30 in the if statement above
}
return 0;
}
✨✨✨ I am a dividing line ✨✨✨
🍔 loop
/ There are things that have to be done all the time, like my practice day after day; like everybody's study day after day.
#include <stdio.h>
int main()
{
int line=0;
printf("Step in C Rivers and lakes\n");
while (line < 20000)
{
printf("Refine a line of code %d\n",line);
line++;
}
printf("You'll get the strongest Union offer");
return 0;
}
✨✨✨ I am a dividing line ✨✨✨
🍔 function
C language, encapsulates some independent functions into a single function
//Sum two numbers
#include <stdio.h>
int a=20;
int main()
{
int num1=0;
int num2=0;
int a=100;
int b=200;
int sum;
scanf("%d%d",&num1,&num2);
sum=num1+num2;
sum=a+b;
printf("sum=%d\n",sum);
return 0 ;
}After a function call is made:
#include <stdio.h>
int a=20;
int Add(int x, int y)// Add function name
{
int z=x+y;
return z;
}
int main()
{
int num1=0;
int num2=0;
int sum;
scanf("%d%d",&num1,&num2);
sum=Add(num1,num2);//sum=num1+num2;
printf("sum=%d\n",sum);
sum=Add(2,4);
printf("sum=%d\n",sum);
return 0 ;
}
✨✨✨ I am a dividing line ✨✨✨
🍔 array
A collection of elements of the same type
🍔 Operator
🍕 Arithmetic Operators
Here's a special introduction to the%-modulo operator
🍕 Shift operators
#include<stdio.h>
int main()
{
//Shift (binary) operator
// << Move Left
// >Move right
int a=1；//Integer 1 takes 32 bits
//00000000 00000000 00000000 00000001
int b = a<<1;//A Move a Binary Bit to the Left
// 00000000 00000000 00000000 000000010
int c = a<<2;
// 00000000 00000000 00000000 000000100
printf("a=%d\n",a);
printf("b=%d\n",b);
printf("c=%d\n",c);
}
🍕 Bitwise operators
(binary) bit operation
#include<stdio.h>
int main()
{
// &Bitwise and
//| Bitwise or
// ^Bitwise XOR
int a = 3;//011
int b = 5;//101
int c = a & b; //The corresponding binary bit has 0 then 0; all 1 is 1
int d = a | b; //The corresponding binary bit has 1 1; all 0 is 0
int e = a ^ b; //The corresponding binary bits are the same 0; the difference is 1
printf("%d\n", c);
printf("%d\n", d);
printf("%d\n", e);
return 0;
}
🍕 Assignment Operators
/=assignment
/==Equality of judgement
int main()
{
int a=10;
a=20;
a=a+10;
a+=10;//Simplify
a=a-20;
a-=20;
a=a&2;
a&=2;
a=a>>2;
a>>=2;
//Composite evaluator
// += -= *= %= /= >>= <<= &= |= ^=
return 0;
}🍕 unary operator
Case 1:! Logical Inverse Operation
Case 2: sizeof
#include <stdio.h>
int main()
{
int a=10;
printf("%d\n",sizeof(a));//4
printf("%d\n",sizeof(int));//4
printf("%d\n",sizeof(10));//The type attribute of 10 is int
printf("%d\n",sizeof a );//Real sizeof can be placed without parentheses
printf("%d\n",sizeof int);//error
int arr[10]={0};
printf("%d\n",sizeof(arr));//Calculate the number of array elements
int sz=0;
sz= sizeof(arr)/sizeof(arr[0]);
printf("%d\n",sz);
//Calculate the number of array elements = the total size of the array / the size of each element
//sizeof calculates the size of the space occupied by a variable or type in bytes
}
Case 3: ~ Operator action (for positive numbers)
Case 4: ~ Operator action (for negative numbers)
· Case 5: ++/--Operator
1.Postposition++.
#include <stdio.h>
int main()
{
int a =10;
int b =a++;//Post++, use first, in++.
printf("a=%d ,b=%d",a,b);
return 0 ;
}
2.Pre++.
#include <stdio.h>
int main()
{
int a =10;
int b =++a;//Pre++, first++, then use
printf("a=%d ,b=%d",a,b);
return 0 ;
}
3. Rear--
#include <stdio.h>
int main()
{
int a =10;
int b =a--;
printf("a=%d ,b=%d",a,b);
return 0 ;
}
4. Front--
#include <stdio.h>
int main()
{
int a =10;
int b =--a;//
printf("a=%d ,b=%d",a,b);
return 0 ;
}
🍕 Cast Operator
🍕 Relational Operators
🍕 Logical Operator
🍕 Conditional operator (trinomial operator) exp1? Exp2:exp3
//exp1? exp2:exp3 - Conditional Operator
//exp--Imagine it as an expression
//If expression 1 is true, expression 2 executes;
//If expression 1 is false, expression 3 executes
#include <stdio.h>
int main()
{
int a =10;
int b =20;
int max=0;
if(a>b)
max=a;
else
max=b;
return 0;
}//exp1? exp2:exp3 - Conditional Operator
//exp--Imagine it as an expression
//If expression 1 is true, expression 2 executes;
//If expression 1 is false, expression 3 executes
#include <stdio.h>
int main()
{
int a =10;
int b =20;
int max=0;
max=(a>b ? a : b);
printf("Larger values are%d\n",max);
return 0;
}
🍕 comma expression
🍕 Subscript Reference Operator[]
This is the end of today's voyage, and the floating shadows on C's Lake end!
Dao Friends! See you tomorrow~
