Thread: For loop with equation?

Alright, so I received an assignment from my teacher to make a program that uses if and for loops to allow the reader to pick to calculate the circumference and area of a circle. The teacher said it needs to list the values with the radius increasing in a for loop from 1 to 20. I have only gotten so far as to create the circle with one radius because the looping is not working (supposedly because the radius has to be plugged into an equation). I have tried to switch some code around and add more, however none of my fixes seem to make much difference. I have hit a brick wall so could somebody please help me?

// *****: This is program lists 20 circumfrence values of a circle and 20 area values of a circle.  Comments are in green text.
// Syntax error = typing error - Does not compile
// Logical error flaw is your reasoning they do compile.
// Runtime error does compile but the program crashes when it runs. (Divide by zero)
// Import some code
 
import TerminalIO.KeyboardReader; //This is a piece of code to read characters from the keyboard.
import java.text.DecimalFormat; //This piece of code is imported so the twoDecimal value will work.
 
class Circle {//This class name matches the file name. 
 
 
	public static void main(String args[]) { //Must have this line in all programs.
 
 
 
	// decimals = double
 
 
	KeyboardReader reader = new KeyboardReader();// Declares an object called reader that takes the form of Keyboard reader.
 
	DecimalFormat twoDecimal = new DecimalFormat("0.00");  //Declares how many decimals that is created.
 
	int i;
 
	double circumference, area, pi, circletype;
 
		System.out.println("Enter the value of Pi.");
 
		pi = reader.readDouble(); //Finds pi
 
		System.out.println("To find the circumfrence of a circle type 1. To find the area of a circle type 2.");
 
		circletype = reader.readDouble(); //Reader decides to find the area or the circumfrence
 
			if(circletype == 1){
 
				for (i=1; i<=20; i=i+1);  //Loop
 
					circumference = (2 * pi * i);
 
			System.out.println("The circumference of a circle with a radius from 1 to 20 is, "+ circumference); //Loop of 20 different values in increasing order
 
			}
 
 
 
	}
}

Use braces with the for loop. And remove the semicolon at the end of the line with "for" in it. Ie all your for loops should look like

for(/* etc */) {
    // code here
}

If your code is not giving the output you expect or intend, say what it *does* do and under what conditions.

Wow thanks I hadn't realized how small the error was. Thanks!

You're welcome. The semicolon "ends" the for loop which is saying "for <whatever> do nothing". Then the other statements execute outside the loop.