How to cast an int array to a double array java?

First of all their are some problems in your code which make it very ineffecient.

1)

for (int i = 0; i <= rows-1; i++) {
    for (int j = 0; j <= columns-1; j++) {
    }

In your inner and outer loop you don't have to use <= sign and subtract 1 from right value. you can use i < rows & j < columns.

2)

if (k>=0) {
    System.out.println(...)
    }

Their is no need to use the if statement as it is always true.

Now coming to your question.

Your can use the Math.round method to round double values into long (can store larger values than int).

    double result = termsLeft[k][0]/termsLeft[k][1];
    long round_result = Math.round(result);

So your final code is below :

import java.util.Scanner;

public class Main {

    public static void main (String[] args) {

        Scanner input = new Scanner (System.in);

        System.out.print("Enter the number of rows: ");
        int rows = input.nextInt();
        System.out.print("Enter the number of columns: ");
        int columns = input.nextInt();

        int [][] studentArray = new int [rows][columns];


        for (int i = 0; i <= rows-1; i++) {
            for (int j = 0; j <= columns-1; j++) {
                if (j==0) {
                    System.out.print("Please enter the number of classes left for student " +(i+1)+ " : ");
                    studentArray[i][j] = input.nextInt();
                }

                else if (j>0) {
                    System.out.print("Enter the number of classes taken per term : ");
                    studentArray[i][j] = input.nextInt();

                    while (studentArray[i][j] >= 6) {
                        System.out.println("The number of classes per term for student " +(i+1)+ " is not valid!");
                        System.out.print("Enter the number of classes taken per term : ");
                        studentArray[i][j] = input.nextInt();
                    }
                }
            }
        }

        divide(studentArray);
    }

    public static void divide(int[][] termsLeft) {
        for (int k = 0; k < termsLeft.length; k++) {
            double result = termsLeft[k][0]/termsLeft[k][1];
            long round_result = Math.round(result);
            System.out.println("Student " +(k+1)+ " has " + round_result + " terms left to graduate.");
        }
    }

}