Вот программа на Python, которая предлагает пользователю ввести инфиксное выражение и выводит результат:

import re
def evaluate_expression(expression):
    # Remove any whitespaces from the expression
    expression = expression.replace(" ", "")
    # Convert the expression to postfix notation
    postfix = infix_to_postfix(expression)
    # Evaluate the postfix expression
    result = evaluate_postfix(postfix)
    return result
def infix_to_postfix(expression):
    # Define the operator precedence
    precedence = {"+": 1, "-": 1, "*": 2, "/": 2}
    # Initialize an empty stack and an empty postfix list
    stack = []
    postfix = []
    # Split the expression into tokens
    tokens = re.findall("[+\-*/()]|\d+", expression)
    for token in tokens:
        if token.isdigit():
            # If the token is a number, append it to the postfix list
            postfix.append(token)
        elif token == "(":
            # If the token is an opening parenthesis, push it to the stack
            stack.append(token)
        elif token == ")":
            # If the token is a closing parenthesis, pop operators from the stack and append them to the postfix list
            while stack and stack[-1] != "(":
                postfix.append(stack.pop())
            stack.pop()  # Discard the opening parenthesis
        else:
            # If the token is an operator, pop operators from the stack and append them to the postfix list
            # until an operator with lower precedence is encountered or the stack is empty
            while stack and stack[-1] != "(" and precedence[token] <= precedence.get(stack[-1], 0):
                postfix.append(stack.pop())
            stack.append(token)
    # Pop any remaining operators from the stack and append them to the postfix list
    while stack:
        postfix.append(stack.pop())
    # Return the postfix expression as a string
    return " ".join(postfix)
def evaluate_postfix(expression):
    # Initialize an empty stack
    stack = []
    # Split the expression into tokens
    tokens = expression.split()
    for token in tokens:
        if token.isdigit():
            # If the token is a number, convert it to an integer and push it to the stack
            stack.append(int(token))
        else:
            # If the token is an operator, pop the top two elements from the stack,
            # perform the operation, and push the result back to the stack
            operand2 = stack.pop()
            operand1 = stack.pop()
            if token == "+":
                result = operand1 + operand2
            elif token == "-":
                result = operand1 - operand2
            elif token == "*":
                result = operand1 * operand2
            elif token == "/":
                result = operand1 / operand2
            stack.append(result)
    # The final result is the top element of the stack
    return stack[0]
# Prompt the user to enter an infix expression
expression = input("Enter an infix expression: ")
# Evaluate the expression and print the result
result = evaluate_expression(expression)
print("Result:", result)

Эта программа использует алгоритм Shunting Yard для преобразования инфиксного выражения в постфиксную запись, а затем вычисляет постфиксное выражение с помощью стека.