Cannot find Symbol: Java [duplicate]

Answer 1

All your functions get arguments named a & b, but work with n & m. Change one of those. For example:

private static int sum(int n, int m)
{
    return n+m;
}

Answer 2

You never defined your input variable in the body of the menu method. Try adding Scanner input = new Scanner(System.in) within the menu method. Simply defining the variable in main does not give menu access to it. If you want to avoid creating a Scanner instance multiple times, you could do something like

import java.util.Scanner;

public class MathMenu {
    private static Scanner input = new Scanner(System.in);
    ...
}

Then you could use input from all of your methods.

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EDIT: I just noticed something similar for m and n: you have to define them within the method in which they are being used, or make them static fields. If it was up to me I'd do it like this:

import java.util.Scanner;

public class MathMenu {
    private static Scanner input = new Scanner(System.in);
    private static int n = 15;
    private static int m = 8;

    // ...
    // your other methods unchanged
    // ...

    public static void main(String[] args) {
        menu(args);  // or just "menu()" if you remove the arguments from the menu method declaration.
    }
}

Answer 3

You didn't define input in your program, but calling

choice=input.nextInt();

Assuming you want to get input from user, you need to have

Scanner input = new Scanner(System.in)  

right before choice=input.nextInt();