Taking a step back to sanity on this one, sorry about the difficulty of lesson 11


Topics Discussed: Using a loop to count something for us.

Source Code for Lesson 12:

import java.util.Scanner;
 class Jtutorial1 {
    public static void main(String args[]){
        Scanner input = new Scanner(System.in);
        /*
        int total=0, countDown=0;
        double average=0;
        
        do{
        System.out.println("Enter a number between 1 and 1000: ");
        countDown=input.nextInt();
        }while(countDown < 1 || countDown > 1000);
        
        
        for(int i=1; i<= countDown; i++){
                total += i;
            System.out.println(i);
        }
        
        average = total / (double)countDown;
        
        
        System.out.println("The total of all the numbers between 1 and "+countDown+ " is "+total+" and the average is: "+average);
        
        
        //(int)x,  (long)x, 
         * /
         */
        String hello="Hello World";
 
        System.out.println("The length of the string hello is: " +hello.length()+ " And contains the words / characters: "+hello );
 
 
    }//end main
}//end class

 

 

HomeWork:

/** See math operations in java here: https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html* Each of these operators can be called like I called Math.pow (ex: Math.abs(variable) )** Problems that you should try to solve-- Pick one or more!* 
A: Allow the user to enter a telephone number, use an if statement to invalidate numbers that are too long / short in length* if the telephone number is within the right length, seperate the numbers appropriately into how they would appear in your* country of origin: Ex. 7818789000 would turn into 781-878-9000 in the USA. (This won't require much but mod / division)* Hint: Use long or double if you need to use a big number.** 
B: Quadratic formula solver: The quadratic equation made each of us a little scared when we first saw it in algebra 1, write* a program that conquers the beast that is the quadratic formula (Google it)* 
C: Write a program that will allow you to input a number to select an operation (output a menu, then allow the user to select one).* In that menu you should be allowing the user to choose a shape (circle, square, rectangle, etc). Once they select it, ask them to* input the dimensions of it (circle can be radius, diameter, circumference, rectangle can be length, width, perimeter or area.... etc etc.)* Once you have taken in a few points of input, calculate the missing pieces of information. Perhaps someone has a rectangle* where they have the area and the length, but not the width. Using java, figure out what the missing width is.** 

D: Extra credit for people that are antsy to get some after the last 2 assignments (grades posted this weekend):* write a program that determines the last digit of 3^n power (3^3 = 27, thus 7). Hint, you can use n%4 to help you on this one.*/

Casting numbers
Casting numbers is an important part of any programming language that has certain roles that numbers fall into. The basic idea is this: assume that you have two numbers that you would like to divide, let’s assume you have 12 items that you want to divide equally among 7 people, assuming that we were to type that problem into java as an integer, we would get the following:

12/7 = 1

We can clearly see that this is wrong, but when you think about it, it’s also right. An integer cannot possibly hold a decimal value, therefore it being > 1.5 does not mean it will be rounded or anything of the sort… everything after the decimal place is truncated and discarded. Thus 1.71 (12/7) becomes 1. The way to have this resolve as we would like is as follows:

12/7.0; // 1.71.....

Now there’s a lot of different ways that you can cast numbers like this, here is a non-complete list of ways that you can cast integers into doubles for a moment:

double a=0, b=0, c=0, d=0, e=0, f=0, g=0;
a = 12/7;
b = 12.0/7;
c = 12/7.0;
d = 12.0/7.0;
e = (double)(12)/7;
f = 12/(double)(7);
g = (double)(12)/(double)(7);
System.out.println("a = "+ a);
System.out.println("b = "+ b);
System.out.println("c = "+ c);
System.out.println("d = "+ d);
System.out.println("e = "+ e);
System.out.println("f = "+ f);
System.out.println("g = "+ g);

The output of the above is as follows:
Program output:
a = 1.0
b = 1.7142857142857142
c = 1.7142857142857142
d = 1.7142857142857142
e = 1.7142857142857142
f = 1.7142857142857142
g = 1.7142857142857142

Using a loop to increment a number
Essentially, we’re taking a number defined outside the scope of the loop and incrementing it by the counter of the loop:

int total=0;
for (int i=0; i<10; i++){
    total += i;
}

In the above example we increment total by using the contents of i each time through the loop. If we preserve i for use outside the loop we can easily find the average by dividing out total by the final value of i.

Last modified: April 9, 2019

Author