Numbers

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
// This main method tests a set of student-written methods.
public class Hw4
{
public static void main(String[] args) throws Exception
{
// Declare main method vars and arrays here.
int [] first = new int[50];
int [] second = new int[50];
System.out.print("Primes per Fifty:\n");
for (int low=0, hi=49; hi < 400; low=hi+1, hi=hi+50)
{
System.out.print(low+"-"+hi+": ");
 printPrimesOnRange(low, hi);
}
System.out.println();
System.out.print("Leap Years per Fifty (Years 1000-2049):\n");
for (int low=1000, hi=1049; hi < 2050; low=hi+1, hi=hi+50)
System.out.print(numberOfLeapYears(low, hi) + " ");
   System.out.println();
readIntsTextFile(first, 35, "june.txt");
System.out.println("\nJune Array: ");
printArray(first, 20);
printArray(first, 32);
readIntsTextFile(second, 30, "april.txt");
System.out.println("April Array: ");
printArray(second, 15);
printArray(second, 25); //
System.out.print("\nLargest: ");
for (int i=3; i<32; i=i+3)
System.out.print(largestInArray(first, i)+" ");
System.out.print(" ----- ");
for (int i=3; i<30; i=i+3)
System.out.print(largestInArray(second, i)+" ");
System.out.print("\nLargest Gaps: ");
for (int i=3; i<32; i=i+3)
System.out.print(largestGapInArray(first, i)+" ");
System.out.print(" ----- ");
for (int i=3; i<30; i=i+3)
System.out.print(largestGapInArray(second, i)+" ");
System.out.println("\n\nTesting complete.");
}
// Students should write their 9 methods below
//method 1
    public static boolean isDivisibleBy (int num, int denom){
            /*
        I need to make a statement that returns false if the demoninator is 
        zero because you cant devide by zero
        */
             if (denom == 0){
                 return false;
             }
             return num % denom == 0; 
                 
        }
    //method 2
    public static boolean isPrime(int x) {          
        if (x <= 1) { // a prime number has to be greater than one
            return false;
        }
        /*
        the method loops through all possible denominators of x that are less 
        than or equal to the square root of x 
        */
        for (int denominator = 2; denominator <= Math.sqrt(x); denominator++) 
        {
            if (isDivisibleBy (x,denominator)) {
                return false;
            }
        }
        return true;
        
     }
    //method 3
    public static void printPrimesOnRange(int start, int finish){
                int count = 0;
                /*
                for this I need a for loop so that every time I encounter a 
                prime number i can increase the count by one
                */
        for(int num = start; num<= finish; num++) {
             if(isPrime(num)) {
                  System.out.print(num + " ");
                  count++;
             }
        }
        System.out.print(count + "\n");
            
             
         }
    // method 4
    public static boolean isLeapYear(int year){
        /*
        for this I decied to set the parameters for if the year wasn't a leap 
        year, and if it was a leap year the year would pass through all the if
        else statements and return true
        */
     if (!isDivisibleBy (year,4)) {
            return false;
        } else if (!isDivisibleBy (year,100)) {
            return false;
        } else if (!isDivisibleBy (year,400)) {
            return false;
        } else {
            return true;
    
        }
   }
    // method 5
    public static int numberOfLeapYears(int startYear, int endYear) {
    int count = 0;
    for (int year = startYear; year <= endYear; year++) {
        if (isALeapYear(year)) {
            count++;
        }
    }
    return count;
  }

    public static boolean isALeapYear(int year) {
    boolean isLeapYear = false;
    /*
    this method is the rules for determining leap years, which state that a 
    year is a leap year if it is divisible by 4 but not divisible by 100, or
    if it is divisible by 400.
    */
    if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
        isLeapYear = true;
    }
    return isLeapYear;
}
    // method 6
    

    public static void readIntsTextFile(int[] a, int n, String fileName) throws FileNotFoundException {
        File file = new File(fileName);
        Scanner scanner = new Scanner(file);
        for (int i = 0; i < n; i++) {
            if (scanner.hasNextInt()) {
                a[i] = scanner.nextInt(); 
                /*
                for this program i represents the line being scanned in the file
                which is why I set it equal to zero so it can start at the 
                first position. Then it reads the line then I use i++ to get the
                program to move to the next line in the file and scan that line.
                */
            }
        } 
    }
    //method 7 
    public static void printArray(int[] a, int n) {
    for (int current = 0; current < n; current++) {
        /*
        for loop that will iterate over each element in the array
        */
        System.out.print(a[current] + " ");
        /*
        this will print out the current libe in the array and add a space after
        for the next thing printed
        */
         }
    System.out.println();
      }
    
    // method 8 
    public static int largestInArray(int[] a, int n) {
    int largest = a[0]; // Initialize largest to first element of array

    for (int current = 1; current < n; current++) {
        if (a[current] > largest) {
            largest = a[current]; // Update largest if a[current] is greater 
            //than the current largest
        }
    }
    return largest;
}
// method 9 
    public static int largestGapInArray(int[] a, int n) {
    int largestGap = 0; // Initialize largest gap to zero

    for (int current = 0; current < n - 1; current++) {
        int gap = Math.abs(a[current+1] - a[current]); /*
        I'm doing using Math.abs() because I wan to calcutate the absoulte 
        difference between the current and the next element being read
        */
       
        if (gap > largestGap) {
            largestGap = gap; // Update largest gap if gap is greater 
                            // than current largest gap
        }
    }

    return largestGap;
}

    
     }