二进制运算符> =，-，*的错误操作数类型

Question

I'm having trouble figuring out how to fix these errors I keep getting for my code

import java.util.Scanner;

public class Unit02Prog1 {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        String name;
        System.out.print("name");
        name = input.next();

        String catagory;
        System.out.print("Catagory");
        catagory = input.next();

        String numWords;
        System.out.print("numWords");
        numWords = input.next();

        int price;

        if (numWords >= 50) {
            price = ((numWords -50) * .08) + 5.00;
            System.out.println("customer:" + name);
            System.out.println("Placed an ad in catagory:" + catagory);
            System.out.println("Ad length is" + numWords + "words, at a price of $" + price);
        }
        else {
            price = numWords * .10;
            System.out.println("customer:" + name);
            System.out.println("Placed an ad in catagory:" + catagory);
            System.out.println("Ad length is" + numWords + "words, at a price of $" + price);
        }

    }
}

These are the lines that are getting the same error but with a different symbol at the end

• if (numWords >= 50) {

  bad operand types for binary operator '<='

• price = ((numWords -50) * .08) + 5.00;

  bad operand types for binary operator '-'

• price = numWords * .10;

  bad operand types for binary operator '*'

How can I fix these

Answer 1

your variable numWords is string, please parse it to integer first for comparing. Then, update price to double as well. Sample code is as per below.

    int numWords;
    System.out.print("numWords");
    numWords = input.nextInt();

    double price;

    if (numWords >= 50) {
        price = ((numWords -50) * .08) + 5.00;
        System.out.println("customer:" + name);
        System.out.println("Placed an ad in catagory:" + catagory);
        System.out.println("Ad length is" + numWords + "words, at a price of $" + price);
    }

Answer 2

numWords is a String , not an int . Parse the String to get an int.

int num_words = Integer.parseInt(numWords);

Answer 3

What you are doing wrong

if (numWords >= 50) {

numWords is a string, and >= only works on numbers.

How to fix

You have 2 options for fixing this:

• Read the number in as a String and convert it to a number

   temp = input.nextLine(); numWords = Integer.parseInt(temp); 

  This way means you can check manually, and do not need to catch an exception if the number is wrong.

• Read the number in as a number straight away

   numWords = input.nextInt(); 

  This way is less code, but you will need to catch a NumberFormatException if the input is not an integer.

Other notes

• You use input.next() a lot, depending on your inputs you may want to use nextLine instead
• You may want to use System.out.printf to clean up your printing code

Answer 4

In this situation you need parse from string to integer. Here you have an example:

String simplenumber= "10";
int num = Integer.parseInt(simplenumber);

In your code:

public static void main(String[] args) { Scanner input = new Scanner(System.in);

    String name;
    System.out.print("name");
    name = input.next();

    String catagory;
    System.out.print("Catagory");
    catagory = input.next();

    String numWords;
    System.out.print("numWords");
    numWords = input.next();

    int price;
    int numWordsInt = Integer.parseInt(numWords);

    if (numWordsInt >= 50) {
        price = (int) (((numWordsInt -50) * .08) + 5.00);
        System.out.println("customer:" + name);
        System.out.println("Placed an ad in catagory:" + catagory);
        System.out.println("Ad length is" + numWords + "words, at a price of $" + price);
    }
    else {
        price = (int) (numWordsInt * .10);
        System.out.println("customer:" + name);
        System.out.println("Placed an ad in catagory:" + catagory);
        System.out.println("Ad length is" + numWords + "words, at a price of $" + price);
    }}