Question

当我输入a，b c的值为1.0,3 1时，答案应该只是，说根是-0.381和-2.62803。我得到了两个答案，我也得到了“没有真正的根源”。我想我以错误的方式使用IF语句。请善意地向我解释我哪里出错了。

import java.util.Scanner;
public class sha {
public static void main(String[] args ){
Scanner input = new Scanner (System.in);

System.out.println("Enter a , b , and c : ");
double a = input.nextDouble();
double b = input.nextDouble();
double c = input.nextDouble();

// the equations 
double discriminant = Math.pow (b , 2) - 4 * a * c;
double root1 = (-b + Math.sqrt(discriminant))/2 * a ;
double root2 = (-b - Math.sqrt(discriminant))/2 * a ;

if (discriminant > 0 ){
System.out.printf("The roots are %8.6f and %8.6f ", root1, root2);
}
if (discriminant == 0 ){
System.out.print("The root is  " +  root1);
}
else  {
System.out.print("There are no real roots ");
}




}
}

Answer 1

试试这个：

if (discriminant > 0 ) {
  System.out.printf("The roots are %8.6f and %8.6f ", root1, root2);
}
else if (discriminant == 0 ) {
  System.out.print("The root is  " +  root1);
}
else {
  System.out.print("There are no real roots ");
}

您的代码目前正在运行如下：

// first if group
if (discriminant > 0 ) {
  System.out.printf("The roots are %8.6f and %8.6f ", root1, root2);
}

// second if group
if (discriminant == 0 ) {
  System.out.print("The root is  " +  root1);
}
// handle everything else for second if group only
else {
  System.out.print("There are no real roots ");
}

应该这样运行：

// one if group
if (discriminant > 0 ) {
  System.out.printf("The roots are %8.6f and %8.6f ", root1, root2);
}
else {
  // second if condition in else statement
  if (discriminant == 0 ) {
    System.out.print("The root is  " +  root1);
  }
  // handle everything else
  else {
    System.out.print("There are no real roots ");
  }
}

Answer 2

您需要在代码中使用if，else if和else。然后，只有控件将只执行一个循环，该条件首先变为true，并忽略其他else if和else循环。否则，条件测试将在所有if循环中发生，并且在条件测试通过时执行循环语句，无论先前的循环语句是否已执行

Answer 3

或许更详细的语法有助于明确这一点：

if discriminant > 0
then
   print ...
end if

if discriminant == 0
then
   print ...
else
   print ...
end if

所以我希望你能看到，只有当判别式不为零且判别式的if语句＆gt;才会应用else部分。 0与第一个if语句无关。

因此，您应该按如下方式重写代码：

if (discriminant > 0 ){
   System.out.printf("The roots are %8.6f and %8.6f ", root1, root2);
}
else if (discriminant == 0 ){
   System.out.print("The root is  " +  root1);
}
else  {
   System.out.print("There are no real roots ");
}

有关详细说明，请参阅here。

Answer 4

你使用两个if和一个else。在这种情况下，首先检查第一个条件。然后下一个if.if出现错误也是控制器在其他地方。

import java.util.Scanner;
public class sha {
public static void main(String[] args ){
Scanner input = new Scanner (System.in);

System.out.println("Enter a , b , and c : ");
double a = input.nextDouble();
double b = input.nextDouble();
double c = input.nextDouble();

// the equations 
double discriminant = Math.pow (b , 2) - 4 * a * c;
double root1 = (-b + Math.sqrt(discriminant))/2 * a ;
double root2 = (-b - Math.sqrt(discriminant))/2 * a ;

if (discriminant > 0 ){
System.out.printf("The roots are %8.6f and %8.6f ", root1, root2);
}
else if (discriminant == 0 ){
System.out.print("The root is  " +  root1);
}
else  {
System.out.print("There are no real roots ");
}




}
}

关于IF声明

4 个答案: