Need help with errors in Add/Subtract Program!

[brookeblood1]

Hello Everyone! I just got started with Java, and other than the basic 'Hello World!" program, I have yet to make a working program.

I am attempting to write a program that asks the user whether they want to add or subtract two numbers, have them input the numbers, and complete the equation. This code successfully worked with just adding OR subtracting, but I believe the if, then statement is what is messing it up. Here is the current code.

import java.util.Scanner ;
public class AddSub {
public static void main (String[] args) {
Scanner input = new Scanner (System.in);
int num1, num2, sum, diff ;
System.out.println ("Type 1 for addition, 2 for subtraction.") ;
if (input.nextInt=1) {
System.out.println ("Enter first number."); num1 = input.nextInt();
System.out.println ("Enter second number."); num2 = input.nextInt();
sum = num1 + num2 ;
System.out.printf ("Sum = %d\n" , sum);
	}
if (input.nextInt=2) {
System.out.println ("Enter first number."); num1 = input.nextInt();
System.out.println ("Enter second number."); num2 = input.nextInt();
diff = num1 - num2 ;
System.out.printf ("Difference = %d\n" , diff);
			}
		}
	}

(Sorry if it's badly formatted..)

When typing 'javac AddSub.java' in Terminal, I get the following errors.

AddSub.java:7: error: cannot find symbol
if (input.nextInt=1) {
         ^
  symbol:   variable nextInt
  location: variable input of type Scanner
AddSub.java:13: error: cannot find symbol
if (input.nextInt=2) {
         ^
  symbol:   variable nextInt
  location: variable input of type Scanner
2 errors

Any help would be greatly appreciated! Thank you!

[awinston]

AddSub.java:7: error: cannot find symbol
if (input.nextInt=1) {
         ^
  symbol:   variable nextInt
  location: variable input of type Scanner
AddSub.java:13: error: cannot find symbol
if (input.nextInt=2) {
         ^
  symbol:   variable nextInt
  location: variable input of type Scanner
2 errors

These errors are telling you that there is not a member of class Scanner named "nextInt". Judging from the rest of your code, I think you know how to fix this problem.

Another problem is that you attempt to compare two integers using "=", but "=" is the assignment operator. You want to use "==" to test if two primitive data types, such as integers, are equal to each other.

[brookeblood1]

Thank you for the reply, but I'm still lost as how to fix the issue. On the second issue you mentioned, I'm assuming it would be fixed by this change in code

(input.nextInt==1)

(= changed to ==)

On the other part of the problem, I have no idea how to fix the errors since I used 'nextInt' in other parts of the code.
eg:

System.out.println ("Enter first number."); num1 = input.nextInt();

Is the use of the If, then statement correct?

[awinston]

Yes, the use of the if-then statement is correct. Edit: However, the user will be prompted for a 1 or 2 a total of 2 times when it should be 1.

Is nextInt() a variable or a method?

[brookeblood1]

I'm pretty sure nextInt() is a method. To fix that from happening twice would I need to keep the first if code, and then change the second to else?

[awinston]

I'm pretty sure nextInt() is a method.

In that case, typing

input.nextInt

...will not call the method because you are missing the parenthesis.

And yes, an if-else statement can solve your problem.

[brookeblood1]

Aha! Easy fix! Thank you very much

Here's the fixed code

import java.util.Scanner ;
public class AddSub {
public static void main (String[] args) {
Scanner input = new Scanner (System.in);
int num1, num2, sum, diff ;
System.out.println ("Type 1 for addition, 2 for subtraction.") ;
if (input.nextInt()==1) {
System.out.println ("Enter first number."); num1 = input.nextInt();
System.out.println ("Enter second number."); num2 = input.nextInt();
sum = num1 + num2 ;
System.out.printf ("Sum = %d\n" , sum);
	}
else {
System.out.println ("Enter first number."); num1 = input.nextInt();
System.out.println ("Enter second number."); num2 = input.nextInt();
diff = num1 - num2 ;
System.out.printf ("Difference = %d\n" , diff);
			}
		}
	}

[Junky]

Notice how you have duplicated the code to enter the numbers in both branches of the if statement. Why not have the code to input the numbers once before the if statement and only use the if statement to do the calculation?