C++基本中の基本その8

※自分用メモ
※引用元「ローベルのC++入門講座」

#include <iostream>
#include <string>
using namespace std;

void obamaTerm(int &x) //int &xを変数にすることで「参照」という変数が作れる。
{
    if(2009 <= x && x <= 2016)
        x -= 2008;
    else
        x = 0;
}

void presidency() //ここのコーディングは結構めんどくさい。。。レベル上げたらもっと綺麗にする。
{
    int year;
    
    cout << "Enter a year: " << flush;
    cin >> year;
    
    obamaTerm(year); //この場合xはyearの参照になり、xを操作することでyearを操作することができる。
    if(year == 1)
    {
        cout << "That year would be Obama's " << year << "st year as president." << endl;
    }

    
   else if(year == 2)
    {
        cout << "That year would be Obama's " << year << "nd year as president." << endl;
    }

    
   else if(year == 3)
    {
        cout << "That year would be Obama's " << year << "rd year as president." << endl;
    }
    
    
    else if(4 <= year && year <= 8)
    {
        cout << "That year would be Obama's " << year << "th year as president." << endl;
    }
    else
    {
        cout << "Obama was not president in that year." << endl;
    }    
}

int main()
{
    presidency();
    presidency();
    presidency();
    presidency();
    presidency();
    
    return 0;
}

結果

Enter a year: 2009
That year would be Obama's 1st year as president. 
Enter a year: 2010
That year would be Obama's 2nd year as president. 
Enter a year: 2011
That year would be Obama's 3rd year as president. 
Enter a year: 2015
That year would be Obama's 7th year as president. 
Enter a year: 1999
Obama was not president in that year.

・int &xとすることで 参照 (pass by reference)という特殊な変数になる。
・参照によって xが yearへの参照になり、関数越しに変数を操作することができる。