C++ Printer Plus 学习笔记第七章函数函数和数组

╰+攻爆jí腚メ 2022-02-13 15:55 188阅读 0赞

函数原型：

0. 函数原型就是 放在int前面声明函数名称，传参类型和返回类型的一个语句

1. 为什么需要函数原型

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2. 原型的语法：

returntype functionname(typename);

3.原型的功能：

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简单的数据类型 正常是按值传递。 而复杂数据类型就是按引用传递

int sum = sum\_arr(int arr\[\], int n) 这边的arr\[\] 不一定指的是数组 也可以是指针 或者数组的第一个元素的地址 其实可以换成 int\* arr

在7.6de  arrfun2.cpp这个代码中要注意一个地方跟书上有出入

#include <iostream>
    const int ArSize = 8;
    int sum_arr(int arr[], int n);
    int main()
    {
      int cookies[ArSize] = {1, 2, 4, 8, 16, 32, 64, 128};
      std::cout << cookies << " = array address, ";
      std::cout << sizeof cookies << " = sizeof cookies\n";
      int sum = sum_arr(cookies, ArSize);
      std::cout << "Total cookies eatenl: " << sum << std::endl;
      sum = sum_arr(cookies, 3);
      std::cout << "First three eaters ate " << sum << " cookies.\n";
      sum = sum_arr(cookies + 4, 4);
      std::cout << "Last four eaters ate " <<sum << " cookies.\n";
      return 0;
    }
    
    int sum_arr(int arr[], int n)
    {
      int total = 0;
      std::cout << arr << " = arr, ";
    // 这里 书上是不带‘&’号 但是我的编译器会报错 6.3版本
      std::cout << sizeof &arr << " = sizeof arr\n";
      for (int i = 0; i < n; i++)
        total = total + arr[i];
      return total;
    }

使用数组区间来传递数组的首尾位置

#include <iostream>
    const int ArSize = 8;
    int sum_arr(const int* begin, const int* endl);
    int main()
    {
      using namespace std;
      int cookies[ArSize] = {1, 2, 4, 8, 16, 32, 64, 128};
      int sum = sum_arr(cookies, cookies + ArSize);
      cout << "Total cookies eaten: " << sum << endl;
      sum = sum_arr(cookies, cookies + 3);
      cout << "First three eaters ate " << sum << " cookies.\n";
      sum = sum_arr(cookies + 4, cookies + 8);
      cout << "Last four eaters ate " << sum << " cookies.\n";
      return 0;
    }
    
    int sum_arr(const int* begin, const int* end)
    {
      const int* pt;
      int total = 0;
    
      for (pt = begin; pt !=end; pt++)
        total = total + *pt;
      return total;
    }

先到这今天 明天继续  指针和const

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