Re: Signing In
 

I have been trying to build a Java program to prompt the user to enter the radius of a circle and the diameter, circumference, and area will be output through a "System.out.printf" statement. I can get the program to prompt for the radius and it will display the diameter, but will not identify the Area or Circumference. I keep getting an error with the Math variable. What could be wrong with this code for Area:
System.out.printf("Area is %d\n", (x * x * math.PI) );

Re: Trouble with area
 

Ahem!

Given only radius gives you all the other data. No need to input.
Circumference = 2 * PI * r
Area = PI * r * r
etc.

I'm also assuming your x is entered as a Floating-Point value.

System.out.printf("Area is %f\n", (x * x * math.PI) );

Re: Trouble with area
 

Thanks, that really cleared up my format for the Area and Circumference, but I am still getting an error for diameter. Honestly, I do not know why. I have eliminated one problem by capitalizing the "M" in Math.PI, but can't get over the diameter issue.

Re: Trouble with area
 

Please post your code!

Re: Trouble with area
 

And also post what error you are getting. If you are successfully reading in the radius, then 2 * radius should give you the diameter without problems as long as the radius is declared as the correct type (i.e. float or double).

Re: Trouble with area
 

Here is the last part of the code for the print out. I do not get any errors when I build the program, but when I run it I get the following:

"Diameter is Exception in thread "main" java.util.IllegalFormatConversionException: f != java.lang.Integer"

System.out.print( "declare radius of circle: " ); // prompt for input
x = input.nextInt(); // read first integer

//display results
System.out.printf("Area is %f\n", (x * x * Math.PI) );// output the Area
System.out.printf("Circumference is %f\n", (2 * x * Math.PI) );// output the circumference
System.out.printf("Diameter is %f\n", (2 * x) );// output the diameter using printf

}//end main
}//end class Circle

Re: Trouble with area
 

Post your entire code! Errors can be misleading without seeing everything in context!

For example if x is an integer or a double it can cause a problem with that printf. The fact that it was multiplied with a float (PI) would make the result a float.

Re: Trouble with area
 

Because x is assigned from an input.nextInt(), I assume it's declared as int, so:
%f requires a floating point value, but 2*x is an integer value. Change the format to %d when you print the diameter, OR change the calculation to 2.0*x so the result is floating point.

Re: Trouble with area
 

Oh Yeah! That worked. I was assigning a floating point value to all of the equations. Problem solved, you guys are fabulous. I want to excel at this stuff, so I have to ask why is there a difference in Area, Circumference, and Diameter in being a floating point value and an integer value.

Re: Trouble with area
 

x is an int. When you do a calc with just integers, the result is an int, but if it's mixed ints and floats, the result is float. Pi is a float. Area and circ. involved Pi, bit diameter didn't.