12강 배열 - 배열의 개념 및 사용

12-1 ) 배열
          
       (1) 배열의 정의
                배열이란?
                     : 같은 자료형의 변수들의 나열된 묶음(그냥이 아닌 나열, 순서대로)
                배열의 사용 목적?
                     : 같은 타입의 변수들의 관리를 편하게 하기 위해서

                 ex ) 학생들의 점수관리(각각 변수에 몇 십개씩 처리하기 힘들다)
                                                (우리반 학생들의 점수로 묶어서 번호대로 나열)
                                                (이 때, 저장되는건 오직 정수형 int로만 저장 및 나열)

       (2) 배열의 사용
                 1) 배열의 선언과 생성

                          1. 타입[ ] 배열명;
                          2. 배열명 = new 타입[길이];
                     => 타입[ ] 배열명 = new 타입[길이];
                             - 배열의 선언과 생성을 동시에 하는 초기화!

배열 사용하는 방법

                      ex)  int[ ] ar;    // 정수형을 묶어놓을 것
                            ar = new int [3];   // 배열에 공간 할당, 정수형 3개 묶어놀 만큼
                          int[ ] ar = new int[3];  // 메모리에 입력 시 정수형 3개 저장가능한 공간 생성

                   2) 배열의 길이와 인덱스
                           배열의 값을 다루기(각각의 요소에 접근) 위해선 인덱스(index)를 사용!
                           배열의 각 요소는 배열명[인덱스]로 변수처럼 사용 가능!

                            인덱스(index) : 배열의 요소들의 위치 값

배열 선언 방법, 초기값 넣는 법

         
                           int[ ] ar = new int[3];
                           ar 묶음에서 첫번째 요소에 접근할래!
                           *ar[첫번째 = 0부터 시작]* 
                              =>배열의 시작번호 : 0부터 시작!! 기억해 둘 것

                           ar [              ][              ][             ]
                                   ar[0]          ar[1]         ar[2]       배열명[위치]

           ar[0] = 10;                         10             11           12 
           ar[1] = 11;               ar  [    ar[0]    ][    ar[1]   ][   ar[2]    ]
           ar[2] = 12;

                    3) 배열의 초기화와 출력
                          : 배열 생성시 배열의 값은 배열의 타입에 해당하는 기본값으로 초기화!

                           정수형 배열의 초기값 : 0
                           문자형 배열의 초기값 : ' '
                           실수형 배열의 초기값 : 0.0
                           문자열 배열의 초기값 : Null

배열 초기화와 배열의 기본값

                  Tip!
                  - 배열명.length : 배열의 길이 구하기
                  - Arrays.toString(배열명) : 배열의 요소를 문자열로 출력

배열을 이용한 평균값구하기