C++ Printer Plus 學習筆記 第七章 函數 函數和數組

函數原型：

0. 函數原型就是 放在int前面聲明函數名稱，傳參類型和傳回類型的一個語句

1. 為什麼需要函數原型

2. 原型的文法：

returntype functionname(typename);

3.原型的功能：

簡單的資料類型 正常是按值傳遞。 而複雜資料類型就是按引用傳遞

int sum = sum_arr(int arr[], int n) 這邊的arr[] 不一定指的是數組 也可以是指針 或者數組的第一個元素的位址 其實可以換成 int* arr

在7.6de  arrfun2.cpp這個代碼中要注意一個地方跟書上有出入

#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, ";
// 這裡 書上是不帶‘&’号 但是我的編譯器會報錯 6.3版本
  std::cout << sizeof &arr << " = sizeof arr\n";
  for (int i = 0; i < n; i++)
    total = total + arr[i];
  return total;
}
           

使用數組區間來傳遞數組的首尾位置

#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;
}
           

先到這今天 明天繼續  指針和const