The C language is used to write an Socket communication program based on the TCP and UDP protocols

Tcp multithreaded server and client programs
Server program:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#define PORT 8082
#define BUFSIZE 512
char buf[BUFSIZE+1];

void* fun(void* x)
{
    //printf("enter thread!\r\n");
    int new_fd=*((int*)x);
  while(1)
    {
    int z=read(new_fd,buf,BUFSIZE);// The first  6  step   Read the socket 
  if(z==0){printf("client close !");break;};
  buf[z]='\0';
  printf("%s\r\n",buf);// print 
  };
}
int newfd[512];
int inewfd=0;
int main()
{
  // The first  1  step   Create a socket 
  int sockfd=socket(AF_INET,SOCK_STREAM,0);
  // The first  2  step   Set the address structure 
  struct sockaddr_in svraddr;
  svraddr.sin_family=AF_INET;// use  internet  agreement 
  svraddr.sin_port=htons(PORT);
  inet_aton("0.0.0.0",&svraddr.sin_addr);
  // The first  3  step   The binding 
  int ret=bind(sockfd,(struct sockaddr*)&svraddr,sizeof(svraddr));
    if(ret<0){printf("error bind!\r\n");exit(-1);};
  // The first  4  step   Listening to the 
  listen(sockfd,128);
  while(1)
  {
  newfd[inewfd++]=accept(sockfd,NULL,NULL); // The first  5  step   receive 
  pthread_t ntid;
    pthread_create(&ntid,NULL,fun,(void*)&(newfd[inewfd-1])); 
  }
}

Note:

gcc server.c -o server -lpthread

Client program cli.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#define PORT 8082
#define BUFSIZE 512
char buf[BUFSIZE+1];
int main()
{
  // The first  1  step   create 1 Individual socket 
  int sockfd=socket(AF_INET,SOCK_STREAM,0);
  // The first  2  step   Set up the  addr  The structure of the body 
  struct sockaddr_in svraddr;
  svraddr.sin_family=AF_INET;// use  internet  agreement 
  svraddr.sin_port=htons(PORT);
  inet_aton("127.0.0.1",&svraddr.sin_addr);
  // The first  3  step   Connect to server 
  connect(sockfd,(struct sockaddr*)&svraddr,sizeof(svraddr));
  while(1)
  {
  scanf("%s",buf);
  write(sockfd,buf,strlen(buf)); // The first  4  step   Writes a string to a socket 
  }
}

Udp server and client programs

Server program:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#define PORT 8082
#define BUFSIZE 512
char buf[BUFSIZE+1];
int main()
{
  // The first  1  step   Create a socket 
  int sockfd=socket(AF_INET,SOCK_DGRAM,0);
  // The first  2  step   Set the address structure 
  struct sockaddr_in svraddr;
  svraddr.sin_family=AF_INET;// use  internet  agreement 
  svraddr.sin_port=htons(PORT);
  inet_aton("0.0.0.0",&svraddr.sin_addr);
  // The first  3  step   The binding 
  int ret=bind(sockfd,(struct sockaddr*)&svraddr,sizeof(svraddr));
  if(ret<0){printf("cannot bind!\r\n");exit(-1);};
  while(1)
  {
        struct sockaddr_in cli;
        int len=sizeof(cli);
    int z=recvfrom(sockfd,buf,BUFSIZE,0,(struct sockaddr*)&cli,&len);// The first  6  step   Read the socket   
    buf[z]='\0';
    printf("%s\r\n",buf);// print 
  }

}

Client program cli.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#define PORT 8082
#define BUFSIZE 512
char buf[BUFSIZE+1];
int main()
{
  // The first  1  step   create 1 Individual socket 
  int sockfd=socket(AF_INET,SOCK_DGRAM,0);
  // The first  2  step   Set up the  addr  The structure of the body 
  struct sockaddr_in svraddr;
  svraddr.sin_family=AF_INET;// use  internet  agreement 
  svraddr.sin_port=htons(PORT);
  inet_aton("127.0.0.1",&svraddr.sin_addr);
  // The first  3  step   Connect to server 
  //connect(sockfd,(struct sockaddr*)&svraddr,sizeof(svraddr));
  while(1)
  {
  scanf("%s",buf);
  sendto(sockfd,buf,strlen(buf),0,(struct sockaddr*)&svraddr,sizeof(svraddr)); // The first  4  step   Writes a string to a socket 
  }
}