功能循环错误的错误

Question

我试图编写一个程序，该程序获取两个用户并计算它们之间的数字总和（加上自己的）。但是我遇到了一个错误！这是我的代码：

import java.util.Scanner;
public class ForLoop {
    public static void main(String[] args) {
        int sum =0;
        System.out.print("Enter first number: ");
        Scanner myScanner = new Scanner(System.in);
        boolean firsttest;
        if(firsttest = myScanner.hasNextInt()) {
            int firstNumber = myScanner.nextInt();
            System.out.print("Enter second number: ");
                boolean secondtest;
                if(secondtest = myScanner.hasNextInt()) {
                    int secondNumber = myScanner.nextInt();
                    for(firstNumber ; firstNumber <= secondNumber ; firstNumber++) {
                        sum = sum + firstNumber ;
                    }
                }else {
                    System.out.println("Second number is not correct format.");
                }
        }else {
            System.out.println("first number is not correct format.");
        }
            System.out.println("total= " + sum);
    }
}

错误：

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
Syntax error on token "firstNumber", ++ expected after this token
at ForLoop.main(ForLoop.java:16)

Answer 1

您不需要此处的for循环的第一部分。该值已经定义，并初始化int firstNumber = myScanner.nextInt();

因此，您想要

for( ; firstNumber <= secondNumber ; firstNumber++) {
    sum = sum + firstNumber ;
}

看起来很奇怪，所以请尝试一段循环

while(firstNumber <= secondNumber)   {
    sum = sum + (firstNumber++);
}

另外， sum += firstNumber++也有效

Answer 2

更改

for(firstNumber ; firstNumber <= secondNumber ; firstNumber++)

to

for(; firstNumber <= secondNumber ; firstNumber++)