help me with my scripts...

[JeffJak]

why my scripts is wrong, i have declare the cost..why i still got
error

// How much it cost for the gas to be consumed per cubic meter
import java.util.Scanner;

public class GasCharge
{
public static void main(String[] args)
{
// Declare constants and variables
double cost;
double gas;

// Read input
Scanner scn = new Scanner(System.in);
System.out.print("The amount of gas consumed in cubic
meters:");
gas = scn.nextDouble();

// Selection Structure

if (gas <= 100)
cost = 5.00;
else
if (gas <=300)
cost = gas * 0.4;
else
if (gas <= 500)
cost = gas * 0.2;
else
if (gas > 500)
cost = gas * 0.1;

// Display output (result)
System.out.println ("The total cost is($):" +cost);
}
}


ERROR->
GasCharge.java:32: variable cost might not have been initialized
System.out.println ("The total cost is($):" +cost);
^
1 error

----jGRASP wedge2: exit code for process is 1.
----jGRASP: operation complete.

Thanks in advance...=)

 

[Tom Hawtin]

double cost;

if (gas <=300)
cost = gas * 0.4;
else
if (gas <= 500)
cost = gas * 0.2;
else
if (gas > 500)
cost = gas * 0.1;

// Display output (result)
System.out.println ("The total cost is($):" +cost);

The definite assignment rules of the Java spec do not take into account
that a number is either less-than-or-equal or greater-than another[1].
You need an else clause (such as "else { throw new Error(); }").

As a matter of style I would always put braces in if-else statements.
The compiler doesn't take any notice of your indentation.

Also it's usual to put else and if on the same line, as:

if (a < b) {
...
} else if (a > b) {
...
} else if (a == b) {
...
} else {
throw new Error();
}

Tom Hawtin

[1] Actually a double can be a NaN (Not a Number) which is neither
greater, equal to or less than any number.

 

[Patricia Shanahan]

JeffJak wrote:
....

if (gas <= 100)
cost = 5.00;
else
if (gas <=300)
cost = gas * 0.4;
else
if (gas <= 500)
cost = gas * 0.2;
else
if (gas > 500)
cost = gas * 0.1; ....
ERROR->
GasCharge.java:32: variable cost might not have been initialized
System.out.println ("The total cost is($):" +cost);
^
1 error

You need to pick a value for cost before you attempt to use it.

Local variables are different from fields. Fields without an explicit
initializer get a default value, 0 for type double.

In deciding whether a variable is "definitely assigned", the compiler is
not permitted to combine conditions. Even if it were, if gas were a
Not-a-Number neither (gas <= 500) nor (gas > 500) would be true.

I would get rid of the last if, and make the final assignment the else
clause for the previous if.

Patricia