CS 1073 -- Arrays and Loops

CS 1073 Introductory Programming
for Scientific Applications
Arrays and Loops

Exam Scores in an Array: This first Java program reads exam scores, similarly to the example Loop Patch. However, this example stores the scores in an array, for use later. The inputting of ints uses the functions in Homework 3: Print a Tree (shown in dark yellow below). All the program below does is to print the scores that were read in.


import java.io.*;

public class Scores {

   // getNextChar: fetches next char
   public static char getNextChar() {
      char ch;
      try {
         ch = (char)System.in.read();
      }
      catch (Exception exception)
      {
         System.out.println("Error reading character");
         ch = ' ';
      }
      return ch;
   }

   // getNextInt: fetches next int.
   public static int getNextInt() {
      char ch = ' '; // = ' ' to keep compiler happy
      int num;  // the number to convert
      int sign = 1; // gives sign of answer
      ch = getNextChar();
      // skip over initial blanks and newlines
      while (ch == ' ' || ch == '\n')
         ch = getNextChar();
      // check for + or - sign
      if (ch == '+') ch = getNextChar();
      if (ch == '-') {
         sign = -1;
         ch = getNextChar();
      }
      // read digits, construct input integer;
      // (same as the method "Integer.parseInt()"  )
      num = 0;
      while (Character.isDigit(ch)) {
         num = num*10 + (ch - '0');
         ch = getNextChar();
      }
      return sign * num;
   }

   public static void main(String[] args) {
      int n = 0;  // number of scores
      int[] s = new int[10]; // array, room for up to 10 scores
      for (;;) {  // infinite loop, terminated by break inside
         int score = getNextInt();
         if (score == -1) break;
         s[n] = score;
         n++;
      }

      for (int i = 0; i < n; i++)  // loop to print scores
         System.out.print(s[i] + " ");

   }
}

Here are results of runs with with two different sets of scores boldface is data entered):

80  90  100  -1
80 90 100

72  85  92  87  -1
72 85 92 87

Working With Data in an Array: Once the scores have been read into an array, they are readily available, and we can do anything we want with them, including calculating their average, the minimum and maximum score, and anything else we can imagine. (The program below doesn't include the two yellow functions above, but they have to be present.)


import java.io.*;
public class Scores {
   // functions getNextChar and getNextInt here 

   public static void main(String[] args) {
      int n = 0;  // number of scores
      int[] s = new int[10]; // array, room for up to 10 scores
      for (;;) {  // infinite loop, terminated by break inside
         int score = getNextInt();
         if (score == -1) break;
         s[n] = score;
         n++;
      }

      for (int i = 0; i < n; i++)  // loop to print scores
         System.out.print(s[i] + " ");
      System.out.println();

      double average;
      int sum = 0;  // needed for average
      for (int i = 0; i < n; i++)  // loop to calculate average
         sum = sum + s[i];
      average = (double)sum/n;
      System.out.println("Average score: " + average);

      int minScore = s[0];
      int maxScore = s[0];
      for (int i = 1; i < n; i++) { // loop to calculate min and max
         if (s[i] > maxScore) maxScore = s[i];
         else if (s[i] < minScore) minScore = s[i];
      }
      System.out.println("Max score: " + maxScore + ", Min score: " + minScore);
   }
}

Here are results of runs with with two different sets of scores boldface is data entered):

80  100  90  -1
80 100 90
Average score: 90.0
Max score: 100, Min score: 80

98  75  83  95  71  88  65  -1
98 75 83 95 71 88 65
Average score: 82.14285714285714
Max score: 98, Min score: 65

CS 1073 Introductory Programming for Scientific Applications Arrays and Loops

CS 1073 Introductory Programming
for Scientific Applications
Arrays and Loops