c getting started 1

1. Header file include < stdio. H >
2. int main(){}
3. gcc compile-o changed to executable name

c getting started 2

2.1 basic data types: character type, integer type and floating point type

• 2.1.1 character type. A single character needs to be enclosed in single quotation marks and placeholder% c
• 2.1.2 integer,% d
• 2.1.3 floating point,% f

2.2 operators: arithmetic operators, relational operators and logical operators

• 2.2.1 arithmetic operator: + - * /% remainder

*/% priority greater than +-

Note:
23% 10 single digits
Ten digits of 23 / 10

• 2.2.2 relational operators = =! = > < > =<=
• 2.2.3 logical operator & & and (both true are true) | or (one true is true)! Non (reverse)
  Priority:! > Arithmetic operators > relational operators > & & >||

2.3 variables

• 2.3.1 type variable name
• 2.3.2 naming rules:

1. Composed of letters, numbers and underscores
2. You can't start with a number
3. Case sensitive
4. The keyword "auto break..." in c language cannot be used

• 2.3.3 variables must be initialized before use!!! (definition and assignment)
  Three elements: type, variable name and value
• 2.3.4 expression (computable formula must have result)
• 2.3.5 input

 int n;
 int a,b;
 scanf ("%d %d %d",&n,&a,&b);

If the remainder is taken, only when the placeholder is written two%%, one will be displayed without error, such as printf ("% d%%% d \ n", a, b);

• 2.5.6 ++n

1. It's a formula, and it's worth it
2. It changes the value of variable n

Note: n + + suffix self increasing / N – the value of self decreasing expression is the original value. After calculation, the value of variable will be automatically increased by one

	Prefix self increment (+ + n)	Prefix subtraction (– n)	Suffix self increment (n + +)	Suffix subtraction (n –)
The value of the expression	n+1	n-1	n	n
Value of variable	n+1	n-1	n+1	n-1

1==n can avoid writing one less = 1=n will u report an error, left value and right value!!! To be added

     stay vim If you want to make up, you can press ctrl+p

c getting started 3

• Switch case: case needs to be followed by integer constant; Break is required for each condition. If there is no break, it will continue to be executed, which is equivalent to the same discrimination method as below;

• 3.2.1 while(){}

Important examples:

#include <stdio.h>

int main(){
//Find all integers between mn
/*  int n,m;
    printf("input n,m:");
    scanf("%d%d",&n,&m);

    while(n<m){
       printf("%d ",++n);
    }
    printf("\n");
*/
   int n;
   scanf("%d",&n);
   //Enter an integer n and find the number of digits of this number. For example, the number of digits of 123 is 3
   int count =0;
   while(0!=n){
       n/=10;
       count++;
   }
   printf("%d\n",count);

   //Enter an integer n and find the sum of each integer
   int m;
   scanf("%d",&m);
   int sum=0;
   while(0!=m){
      sum+=m%10;
      m=m/10;
   }
   printf("sum=%d\n",sum);

   //Enter an integer to reverse the number bit by bit.
   int a;
   scanf("%d",&a);
   int sum2=0;
   while(0!=a){
      sum2=sum2*10+a%10;
      a/=10;
   }
   printf("sum2=%d\n",sum2);
}

• 3.2.2
  Difference between do while and while (send proposition):
  Do while is to cycle before judgment, and the loop body is executed at least once.
  while is to judge before execution. The loop body may not be executed at all.
• 3.2.3 for statement
  For (initial value; condition; increment or decrement) {}

Example:

#include<stdio.h>

int main(){
    int n;
    scanf("%d",&n);
    int sum=0;
    int res=1;

    for(int i=0;i<n;++i){
       int m;
       scanf("%d",&m);
       sum+=m;
       res*=m;
    }
    printf("sum=%d\n",sum);
    printf("multi=%d\n",res);
    printf("average=%d\n",sum/n);
}

• 3.2.4 break and continue statements
  In while and for, break is to end the whole loop body, and continue is to end a single loop

Example code:

#include<stdio.h>

int main(){
  
    //Print the first ten ordinary years of the 21st century
    int count =10;
    for(int i=2000;i<2100;++i){
        if(i%4==0&&i%100!=0||i%400==0)continue;
        printf("%d\n",i);
        --count;
        if(0==count)break;
    }
    *
    //Print the first ten leap years of the 21st century
    int count2 =10;
    for(int i=2000;i<2100;++i){
        if(i%4==0&&i%100!=0||i%400==0){
        printf("%d\n",i);
        --count2;
        if(0==count2)break;
        }
}
}

• 3.3.1 there is only one statement in if, while and for, and large brackets can be omitted
• 3.3.2 ternary operator:?

 days=(year%4==0&&year%100!=0||year%400==0)?29:28;