1.分别开发TCP客户端与服务端，客户端从键盘输入一个四则运算表达式（如“1+2”、“6/3”等）并发送给服务端。服务端接收后执行运行，并将结果返回给客户端。详见参考代码。

以下是Python实现TCP客户端与服务端，客户端从键盘输入一个四则运算表达式并发送给服务端，服务端接收后执行运算，并将结果返回给客户端的代码：

服务端代码：

import socket

def calculate(expression):
    try:
        result = eval(expression)
        return str(result)
    except:
        return "Error: Invalid expression"

HOST = '127.0.0.1'
PORT = 8888

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind((HOST, PORT))
server_socket.listen(1)

print('Server is running on %s:%s' % (HOST, PORT))

while True:
    conn, addr = server_socket.accept()
    print('Connected by', addr)
    while True:
        data = conn.recv(1024)
        if not data:
            break
        expression = data.decode()
        print('Received expression:', expression)
        result = calculate(expression)
        conn.sendall(result.encode())
    conn.close()
    print('Connection closed')

客户端代码：

import socket

HOST = '127.0.0.1'
PORT = 8888

client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client_socket.connect((HOST, PORT))

while True:
    expression = input('Please enter an expression (q to quit): ')
    if expression == 'q':
        break
    client_socket.sendall(expression.encode())
    result = client_socket.recv(1024).decode()
    print('Result:', result)

client_socket.close()