帮我用C语言做一个功能相对完整的四则运算系统

好的，这是一份功能相对完整的四则运算程序的代码：

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char operator;
    double firstNumber, secondNumber;

    printf("请输入两个数和一个运算符 (+, -, *, /): ");
    scanf("%lf %lf %c", &firstNumber, &secondNumber, &operator);

    switch (operator)
    {
        case '+':
            printf("%.1lf + %.1lf = %.1lf", firstNumber, secondNumber, firstNumber + secondNumber);
            break;

        case '-':
            printf("%.1lf - %.1lf = %.1lf", firstNumber, secondNumber, firstNumber - secondNumber);
            break;

        case '*':
            printf("%.1lf * %.1lf = %.1lf", firstNumber, secondNumber, firstNumber * secondNumber);
            break;

        case '/':
            if (secondNumber == 0)
            {
                printf("除数不能为 0");
            }
            else
            {
                printf("%.1lf / %.1lf = %.1lf", firstNumber, secondNumber, firstNumber / secondNumber);
            }
            break;

        default:
            printf("无效的运算符");
    }

    return 0;
}

这段代码可以实现加减乘除四则运算，并且对于除数为零的情况进行了特殊处理。希望这对你有帮助。