Java Error 'error: cannot find symbol'

Question

I am in the process of learning Java. Below is the program that I've been trying to compile, but cannot figure out why 'x' in line 38 provides the following error: 'cannot find symbol'. Any help would be greatly appreciated.

import java.util.Scanner; class metropolis_HW2_7 { static int count = 0; public static void main(String[] args) { double a = 0.; double b = Math.PI; Scanner sc = new Scanner(System.in); while (true) { System.out.println(" Number of bins?"); int nbin = sc.nextInt(); if (nbin < 1) System.exit(0); double[] bin = new double[nbin]; System.out.println(" Number of histories to run?"); int N = sc.nextInt(); double dx = (b - a) / nbin; for (int i = 0; i < N; i++) { if (count == 0) { double squiggle1 = Math.PI * Math.random(); double squiggle2 = Math.PI * Math.random(); double y_1 = 2 * squiggle1 + Math.sin(squiggle1); double y_2 = 2 * squiggle2 + Math.sin(squiggle2); if (y_2 < y_1) { squiggle1 = squiggle2; double x = squiggle2; } else { squiggle1 = squiggle1; double x = squiggle2 / squiggle1; } count++; } else { double squiggle1; double x = Sample(squiggle1); } int binNumber = (int) ((x - a) / dx); bin[binNumber] += 1.; } double x = a - dx / 2.; for (int i = 0; i < nbin; i++) { x += dx; bin[i] /= N * dx; System.out.printf(" Bin %1$5d Sample for x = %2$7.5f is %3$7.5f vs %4$7.5f Ratio (%5$f) \n", i, x, bin[i], PDF(x), bin[i] / PDF(x)); } } } static double Sample(double squiggle1) { double squiggle2 = Math.PI * Math.random(); double y_1 = 2 * squiggle1 + Math.sin(squiggle1); double y_2 = 2 * squiggle2 + Math.sin(squiggle2); if (y_2 < y_1) { squiggle1 = squiggle2; return squiggle2; } else { squiggle1 = squiggle1; return squiggle2 / squiggle1; } count++; } static double PDF(double x) { return (2 * x + Math.sin(x)) / (Math.pow(Math.PI, 2) + 2); } }

Crossposted at coderanch.com/t/645832/java/java/…

maneesh
– maneesh

2015-02-09 06:17:16 +00:00
Commented Feb 9, 2015 at 6:17 — maneesh
– maneesh, Commented Feb 9, 2015 at 6:17

Stack Exchange Broke The Law · Accepted Answer · 2015-02-09 05:09:01Z

Variables only exist inside the scope (between { and }) they're declared in. You have three different variables called x, and none of them exist when the line int binNumber=(int)((x-a)/dx); is executed.

Declare a variable outside the if statements, and then assign it inside it, something like this: (I've removed most of your code to make this example clearer; obvious you still need it)

double x; if (count==0) { if (y_2<y_1) { x=squiggle2; } else { x=squiggle2/squiggle1; } } else { x=Sample(squiggle1); } int binNumber=(int)((x-a)/dx);

manikandan · Accepted Answer · 2015-02-09 05:22:14Z

Declare double x variable globally.You are declared in else part thats why it could not find the variable.

Scope variable Example:

 int a = 80; // Create a global variable "a" void setup() { size(640, 360); background(0); stroke(255); noLoop(); } void draw() { // Draw a line using the global variable "a" line(a, 0, a, height); // Create a new variable "a" local to the for() statement for (int a = 120; a < 200; a += 2) { line(a, 0, a, height); } // Create a new variable "a" local to the draw() function int a = 300; // Draw a line using the new local variable "a" line(a, 0, a, height); // Make a call to the custom function drawAnotherLine() drawAnotherLine(); // Make a call to the custom function setYetAnotherLine() drawYetAnotherLine(); } void drawAnotherLine() { // Create a new variable "a" local to this method int a = 320; // Draw a line using the local variable "a" line(a, 0, a, height); } void drawYetAnotherLine() { // Because no new local variable "a" is set, // this line draws using the original global // variable "a", which is set to the value 80. line(a+2, 0, a+2, height); }

Kon · Accepted Answer · 2015-02-09 05:07:43Z

The variable x is not declared in the scope in which it is used at that line. You are defining and assigning the double x inside two different if-blocks. Try declaring the variable in a broader scope (say, before the if-block, then assign it locally. Then it will be accessible in all 3 places.

Here's a simple example to explain what I mean:

void method() { if (2 > 1) double x = 2; else double x = 3; System.out.println(x); //ERROR, because x is out of scope }

So change it to

void method() { double x = 0; if (2 > 1) x = 2; else x = 3; System.out.println(x); //No error; x is referenced in the same scope in which it is declared }

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