java If-else错误我不理解这个错误

Question

我不明白这个错误是逻辑错误还是其他什么这里是编码“这个程序应该将里亚尔转换成用户使用multiway if else选择的货币

import java.util.Scanner;

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

        double riyal, c;
        int opp;

        System.out.println("Please enter the amount of money in Riyal: ");
        riyal= kb.nextDouble();

        System.out.println("Enter the currency option(1- Dollar, 2- Euro, 3- Yen): ");
        opp= kb.nextInt();

        if(opp==1)

            c=riyal*0.267;
        System.out.print(riyal+" Riyals is converted to "+c" Dollars");

        else if (opp==2)

            c=riyal*0.197;  
            System.out.print(riyal+" Riyals is converted to "+c" Euros");

         else if (opp==3)

            c=riyal*0.27.950;
          System.out.print(riyal+" Riyals is converted to "+c" Yens");

         else
         {
            System.out.println("Invalied opption");
        }
    }
}

错误消息：

error: illegal start of expression
error: 'else' without 'if'
error: ';' expected
error: ')' expected

我正在使用的程序是Jcreator

Answer 1

您没有标记if语句体的开始和结束-wihch意味着它们只是单个语句。您目前有效地获得了：

if(opp==1) {
    c=riyal*0.267;
}
System.out.print(riyal+" Riyals is converted to "+c" Dollars");
else if (opp==2)

正如您所看到的，else不属于任何if块。我强烈建议您始终使用大括号，即使对于单个语句if体：

if(opp==1) {
    c=riyal*0.267;
    System.out.print(riyal+" Riyals is converted to "+c" Dollars");
} else if (opp==2) {
    ...
} // etc

请注意，如果让IDE格式化代码，这一切都会变得更加清晰。IDE将应用的缩进将向您展示如何理解事物

Answer 2

如果if块包含多条语句，则应使用大括号：

if(opp==1) {
    c=riyal*0.267;
    System.out.print(riyal+" Riyals is converted to "+c" Dollars");
} else if (opp==2) {    
    c=riyal*0.197;  
    System.out.print(riyal+" Riyals is converted to "+c" Euros");       
} else if (opp==3) {             
    c=riyal*0.27.950;
    System.out.print(riyal+" Riyals is converted to "+c" Yens"); 
} ... and so on ...

如果不使用大括号编写，则相当于：

if(opp==1) {
    c=riyal*0.267;
}
System.out.print(riyal+" Riyals is converted to "+c" Dollars");

else if (opp==2)

因此else if与任何if无关

Answer 3

if、else和其他流控制语句对它们后面的语句进行操作。如果有多个块，则使用块（{}）：

if(opp==1) {
    c=riyal*0.267;
    System.out.print(riyal+" Riyals is converted to "+c" Dollars");
}
else if (opp==2) {
// ...