C语言编写一个客户端和服务器端程序，客户端连接到服务器端后，请求一个文档，然后显示结果。

好的，这是一个比较典型的客户端和服务器端的网络编程实现。我可以提供一个简单的代码示例，供你参考。

服务器端程序：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <fcntl.h>

#define PORT 8080
#define MAXLINE 1024

int main() {
    int sockfd, new_sockfd;
    char buffer[MAXLINE];
    struct sockaddr_in servaddr, cliaddr;

    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(PORT);

    bind(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr));
    listen(sockfd, 5);

    printf("Server running on port %d\n", PORT);

    while(1) {
        socklen_t len = sizeof(cliaddr);
        new_sockfd = accept(sockfd, (struct sockaddr*)&cliaddr, &len);

        int pid = fork();
        if(pid == 0) {
            close(sockfd);
            memset(buffer, 0, sizeof(buffer));
            read(new_sockfd, buffer, sizeof(buffer));
            printf("Request received: %s\n", buffer);

            int fd = open(buffer, O_RDONLY);
            if(fd == -1) {
                write(new_sockfd, "File not found", strlen("File not found"));
                close(new_sockfd);
                exit(0);
            }

            memset(buffer, 0, sizeof(buffer));
            int n = read(fd, buffer, sizeof(buffer));
            write(new_sockfd, buffer, n);

            close(fd);
            close(new_sockfd);
            exit(0);
        } else {
            close(new_sockfd);
        }
    }

    return 0;
}

客户端程序：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <netinet/in.h>

#define PORT 8080
#define MAXLINE 1024

int main() {
    int sockfd;
    char buffer[MAXLINE];
    struct sockaddr_in servaddr;

    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(PORT);
    inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr);

    connect(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr));

    printf("Enter the file name: ");
    memset(buffer, 0, sizeof(buffer));
    scanf("%s", buffer);

    write(sockfd, buffer, strlen(buffer));

    memset(buffer, 0, sizeof(buffer));
    read(sockfd, buffer, sizeof(buffer));
    printf("Response: %s\n", buffer);

    close(sockfd);

    return 0;
}

这个例子中，客户端程序连接到服务器端，请求一个文件名，并发送给服务器端。服务器端接收到请求后，打开文件，读取文件内容，然后将文件内容返回给客户端。客户端接收到响应后，输出文件内容。

请注意，以上代码仅供参考，实际使用时还需要进行错误处理等优化。