₦airaland Forum

Hey guys, this thread is created by me, for learning and posting the problems en-counted by me during my personal
programming lectures ..I would be posting the difficulty I'm having while learning the Almighty JAVA, and I hope I would be helped.
The book I'm currently using is INTRODUCTION TO JAVA PROGRAMMING 8TH EDITION Y Daniel Liang.

The problems I had so far are:

1: Solved!!
How do you generate a random integer i such that 0 <= i < 20.
Answer: I invoked this statement
double i = Math.random()*20;
System.out.println((int) i);
2. Unsolved:
How do you generate a random integer i such that 10 <= i < 20 [Do not Use conditional Statement].
3. Unsolved:
How do you generate a random integer i such that 10 <= i <= 50 [Do not use conditional Statement].


Please do any one have the idea? if so, kindly explain how, on this thread.

Known_pal: 2. Unsolved:
How do you generate a random integer i such that 10 <= i < 20 [Do not Use conditional Statement].

10 + (int) (Math.random() * 10)

Known_pal: 3. Unsolved:
How do you generate a random integer i such that 10 <= i <= 50 [Do not use conditional Statement].

10 + (int) (Math.random() * 41)

codeaddict: 10 + (int) (Math.random() * 10)


10 + (int) (Math.random() * 41)

Wow, worked. Thanks man. The '10' before them should mean the starting point of possible numbers to be printed.
Thanks for your time.

Please note that I would be posting any Java problems I have on this thread than creating a new thread, please follow this thread.

codeaddict: 10 + (int) (Math.random() * 41)

Sorry i do not understand how this is so. Where did 41 come from?
Thanks

Johnpaul88: Sorry i do not understand how this is so. Where did 41 come from?
Thanks

Math.random() returns a floating point number in the range 0 <= x < 1
So the highest integer value you get, when you multiply with 41 is 40, since int casting truncates the decimal digits.

Unresolved!:


import java.util.Scanner;
class AlgebraCalc {
public static void main (String args[]){
int a,b,c;
double r1,r2;
Scanner input = new Scanner (System.in) ;
System.out.print("Enter a , b , c respectively: " ;
a = input.nextInt();
b = input.nextInt();
c = input.nextInt();

r1 = -b + Math.pow(b * b - 4 * a * c, 0.5)/ 2 * a;
r2 = -b - Math.pow(b * b - 4 * a * c, 0.5) /2 * a;

if ((b * b - 4 * a * c) > 0)
System.out.println("The roots are " + r1 + " and " + r2 );
else if ((b * b - 4 * a * c) < -1)
System.out.println("The root is " + r2 );
else
System.out.println("No Real Roots" );
}
}

After Compiling, the result I got was "The root is NaN" though I used 1 2 3 as my a b c. Any Help and corrections?

A lot of things could cause that. One of the more prominent causes in your code is trying to find the root of a negative number

Known_pal: Unresolved!:


import java.util.Scanner;
class AlgebraCalc {
public static void main (String args[]){
int a,b,c;
double r1,r2;
Scanner input = new Scanner (System.in) ;
System.out.print("Enter a , b , c respectively: " ;
a = input.nextInt();
b = input.nextInt();
c = input.nextInt();

r1 = -b + Math.pow(b * b - 4 * a * c, 0.5)/ 2 * a;
r2 = -b - Math.pow(b * b - 4 * a * c, 0.5) /2 * a;

if ((b * b - 4 * a * c) > 0)
System.out.println("The roots are " + r1 + " and " + r2 );
else if ((b * b - 4 * a * c) < -1)
System.out.println("The root is " + r2 );
else
System.out.println("No Real Roots" );
}
}

After Compiling, the result I got was "The root is NaN" though I used 1 2 3 as my a b c. Any Help and corrections?

If u do the calculation with hand, u will see that with ur input 1,2,3, the Math.pow(...) Will find d squareRoot of (-eight) which is NOT A NUMBER (NAN). Try to change the input value to like ( a is 10, b is 1 and c is 2) to comfirm.

Thanks guys, would give you feed back. Wanna try solving it with paper and pencil then compile it.

I've corrected it. I changed the (< -1) to (<0) so it print out the The equation has no real roots (1 2 3).

And I changed the pattern Java uses by overriding the precedence with parenthesis. Thanks codeaddict and jboy.