Raspberry pie preliminary use

One 、 Create a new user

Create user ：

sudo useradd -m  user name 

Set the password ：

sudo passwd  user name 

Give users sudo jurisdiction （ The following file transfer needs ）:

# Switch to root user
sudo su
# Edit profile
vi /etc/sudoers
# Increase the configuration （ Press i Start editing ,Esc Exit the editor ,:wq! Save forced exit ）, In the open configuration file , find root ALL=(ALL) ALL, Add a line below
# among xxx Is the name of the user you want to join
xxx ALL=(ALL) ALL

Two 、C Program practice

1. Create a c Program

vi  file name .c

2. Get into vi Edit mode , Press i Start writing code

#include <assert.h>
#include <stdio.h>
 
int main()
{
   int a;
   char str[50];
     
   printf(" Please enter an integer value ： ");
   scanf("%d", &a);
   assert(a >= 10);

   printf(" The integer entered is ： %d\n", a);
    
   printf(" Please enter the string ： ");
   scanf("%s", str);
   assert(str != NULL);

   printf(" The input string is ： %s\n", str);
    
   return(0);
}

3. Press Esc Exit edit mode , Input :wq（ Means save and exit ）
4. compiler

 First program name .c It's the code just written , The second program name is where the code results are output 

gcc  The program name .c -o  The program name 

5. Run the program

 A program name of the second in the previous step 

./ The program name 

3、 ... and 、assert() understand

brief introduction

C Standard library assert.h The header file provides a file named assert The macro , It can be used to verify the assumptions made by the program , And output the diagnostic message when it is assumed to be false .

Library macro

assert.h The header file defines a unique function ：assert（）

void assert(int expression)  This is actually a macro , Not a function , Can be used in  C  Add diagnostics to the program .

C Library macro - assert()

describe ：C Library macro void assert(int expression) Allows diagnostic information to be written to the standard error file . let me put it another way , It can be used in C Add diagnostics to the program .
Statement ：void assert(int expression);
expression ： This can be a variable or anything C expression . If expression by TRUE,assert() Do nothing . If expression by FALSE,assert() Will be in standard error stderr An error message appears on the , And stop the program execution .
Return value ： nothing

example ：

#include <assert.h>
#include <stdio.h>
 
int main()
{
   int a;
   char str[50];
     
   printf(" Please enter an integer value ： ");
   scanf("%d", &a);
   assert(a >= 10);

   printf(" The integer entered is ： %d\n", a);
    
   printf(" Please enter the string ： ");
   scanf("%s", str);
   assert(str != NULL);

   printf(" The input string is ： %s\n", str);
    
   return(0);
}

 If the entered integer is greater than or equal to 10, The input string is not empty , The program will continue to run ; If the conditions are not met, the program terminates 

Four 、 Different Linux File transfer between systems

If in Ubuntu File transfer between system and raspberry pie system

scp Command Introduction

Linux scp The command is used for Linux Copy files and directories between .
scp yes secure copy Abbreviation , scp yes linux Based on ssh Log in for secure remote file copy command .
scp It's encrypted. ,rcp It's not encrypted ,scp yes rcp The enhanced .

application （ Will raspberry pie just created .c File transfer to Ubuntu Next ）：

sudo scp test.c [email protected]:/home/xjc/

And then execute scp command , You can successfully upload