1. JavaScript programming questions
What is the difference between null and undefined?
The undefined type has only one value, undefined. When the declared variable has not been initialized, the default value of the variable is undefined.
The null type also has only one value, which is null. null is used to represent an object that does not yet exist, and is often used to indicate that a function attempts to return an object that does not exist.
2. MySQL programming questions
table name students
Find out the student numbers and names of all students who only took one course.
SELECT sno,username,count(course) FROM students GROUP BY sno,username HAVING count(course) = 1;
3. Java programming questions
Print out all the "Daffodil Numbers", the so-called "Daffodil Numbers" refers to a three-digit number whose cubic sum of the digits is equal to the number itself. For example: 153 is a "daffodil number" because 153=1 cubed + 5 cubed + 3 cubed.
package exercise;
public class exercise09 {
public static void main(String[] args) {
for (int num = 100; num < 1000; num++) {
int a = num % 10;// one digit
int b = num / 10 % 10;// ten digit
int c = num / 100 % 10;// hundreds digit
if (Math.pow(a, 3) + Math.pow(b, 3) + Math.pow(c, 3) == num) {
System.out.println(num);
}
}
}
}