四则运算表达式求值普通代码

四则运算表达式的求值通常涉及到基本的算术操作，比如加法、减法、乘法和除法。下面是一个简单的Python代码示例，它使用递归解析器来计算字符串形式的四则运算表达式：

def evaluate_expression(expression):
    def apply_operator(operators, values):
        operator = operators.pop()
        right = values.pop()
        left = values.pop()
        if operator == '+':
            return left + right
        elif operator == '-':
            return left - right
        elif operator == '*':
            return left * right
        elif operator == '/':
            return int(left) / int(right)  # 确保结果是整数

    def greater_precedence(op1, op2):
        precedence = {'+': 1, '-': 1, '*': 2, '/': 2}
        return precedence[op1] > precedence[op2]

    operators = []
    values = []
    i = 0
    while i < len(expression):
        if expression[i].isdigit():
            j = i
            while j < len(expression) and expression[j].isdigit():
                j += 1
            values.append(int(expression[i:j]))
            i = j
        else:
            if i > 0 and expression[i-1] != ' ':
                operators.append(expression[i])
            i += 1

    while operators:
        op = operators[0]
        if not operators or not greater_precedence(op, operators[0]):
            values.append(apply_operator(operators, values))
        else:
            operators.insert(0, op)

    return values[-1]

# 示例
expression = "3 + 5 * 2"
result = evaluate_expression(expression)
print(f"表达式 {expression} 的结果是：{result}")