public class UseArray {

static double[] root2 = new double[100];

static double getRoot(int i){

if(root2[i] == 0){

root2[i] = Math.sqrt(i);

}

return root2[i];

}

public static void main(String args[]){

String pop = "Yesterday all my troubles seemed so far away" +

"Now it looks as though they're here to stay" +

"Oh, I believe in Yesterday" +

"Suddenly I'm not half the man I used to be";

pop = pop.toLowerCase();

int[] alpha = new int[26];

for(int a : alpha) System.out.print(a);

System.out.println();

for(int i=0; i< pop.length(); i++){

char ch = pop.charAt(i);

if(ch >= 'a' && ch <= 'z'){

alpha[ch - 'a']++;

}

}

for(int i=0; i < alpha.length; i++){

char ch = (char)(i + 'a');

System.out.println(ch + ":" + alpha[i]);

}

int[] arDays = {0,31,28,31,30,31,30,31,31,30,31,30,31};

int month = 5;

int days = arDays[month];

System.out.println(month + " 월은 " + days + "일까지 있습니다.");

int score = 5;

String[] message = {

"",

"최고의 성적입니다. 축하합니다.",

"우수한 성적입니다.",

"보통입니다.",

"다소 부진합니다. 더 노력하세요.",

"왜 사니?"

};

int[] rank = {5, 4, 4, 3, 3, 3, 2, 2, 2, 1, 1};

System.out.println(message[rank[score]]);

double[] root1 = new double[100];

for(int i=0; i<100; i++){

root1[i] = Math.sqrt(i);

}

System.out.println("2의 제곱근 : " + root1[2]);

System.out.println("2의 제곱근 : " + getRoot(2));

System.out.println("5의 제곱근 : " + getRoot(5));

System.out.println("2의 제곱근 : " + getRoot(2));

int sum = 0;

for(int i=0; i< args.length; i++){

sum += Integer.parseInt(args[i]);

}

System.out.println("총합계 = " + sum);

int[][] scores = {

{77, 56, 70, 82},

{99, 96, 89, 88},

{81, 69, 62, 80}

};

int classSum = 0;

for(int student = 0; student < scores.length; student++){

sum = 0;

for(int subject = 0; subject < scores[0].length; subject++){

sum += scores[student][subject];

}

System.out.println( (student + 1) + "번 => 총점 : " + sum + ", 평균 : " + (float)sum/scores[0].length );

classSum += sum;

}

System.out.println();

sum=0;

for(int i=0; i<scores[0].length; i++){

sum = 0;

for(int k=0; k<scores.length; k++){

sum += scores[k][i];

}

System.out.println((i+1) + "번 과목의 총점 : " + sum + " 평균 : " + (float)sum/scores.length);

}

}

}