在java中，我如何检查用于输入成绩的数组的输入验证（不能为负数，不能超过100）

Question

So far I've tried to create a while loop that only kicks out if the entered array value is a "correct" one (between 0 and 100). Wich means that the loop should repeat if the value entered is a negative number or something random like a char.

My code so far only works if all grades entered are incorrect. If I enter a 0, 100, and -2 it still goes through, even though -2 should cause the loop to repeat. What do I need to modify to only allow values that are between 0 and 100 to be entered into the array?

Code so far:

//Input validation for grades
int g = 0;

while(g >= 0)
{
  System.out.print("Please Enter the Students' Grades: ");
  for (int c = 0; c < studentGrades.length; c++)
  {
    studentGrades[c] = input2.nextInt();

    if (studentGrades[c] >= 0 && studentGrades[c] <= 100)
    {
       g = -1;
    }
  }
}

Answer 1

In this code snippet:

studentGrades[c] >= 0 && studentGrades[c] <= 100

... you are saying that if the entered grade is greater than or equal to 0 and it is less than or equal to 100, set g to -1 (and exit the loop).

So essentially, every time a valid grade is entered, your loop will exit. You've done the opposite of what you wanted. Try adding a ! before your condition to negate it.

Answer 2

This should do

     outer:
        while(g >= 0) {
            System.out.print("Please Enter the Students' Grades: ");

            for (int c = 0; c < studentGrades.length; c++) {
                studentGrades[c] = input2.nextInt();
                System.out.println(" input is "+studentGrades[c]);
                if (studentGrades[c] <= 0 || studentGrades[c] >= 100) {
                    break outer;
                }
            }
        }

Answer 3

Move your while loop inside the for loop , because I guess you want to validate your input grade for each index : -

And your condition should be g < 0 . Also, you have used reverse condition in your if. You were setting g = -1 for correct input. You need to change your condition in if .

for (int c = 0; c < studentGrades.length; c++) {

    g = -1; // Set to invalid to get your while run first time.

    while(g < 0) {
        System.out.print("Please Enter the Students' Grades: ");
        studentGrades[c] = input2.nextInt();

        // Check invalid grade -> negative or more than 100
        if (studentGrades[c] < 0 || studentGrades[c] > 100) {
            g = -1;

        } else {
            // Break while if correct grade has been entered. Continue with next index
            break;  
        }
    }
}

Answer 4

Put a check before you add the next into the array. If it's out of bounds, ask for another value.

Answer 5

You need to flip the logic around, currently your g flag starts as "invalid" (meaning that if g doesn't change, the loop continues), and when you find a valid grade you mark g as valid.

Instead, at the top of the while loop set g to -1 , and then set it back to 0 if any of the grades provided are invalid, for example:

int g = 0;
while(g >= 0) {
    g = -1;
    System.out.print("Please Enter the Students' Grades: ");
    for (int c = 0; c < studentGrades.length; c++) {
        studentGrades[c] = input2.nextInt();
        if (studentGrades[c] < 0 || studentGrades[c] > 100) {
            g = 0;
        }
    }
}

Answer 6

I think this what you are trying to achieve (also you can enhnace it)

int[] values = new int[5]; //modify this according to your size
int index = 0;
do {
    int value;
    do {
        System.out.println("Enter value " + (index + 1) + ": ");                
        value = input.nextInt();
    } while (value < 0 || value > 100); //make sure each value is valid
    values[index++] = value; //add value to the array
} while(index < values.length); //make sure you get all the values

If for loop is not required then I think it looks better that way.

Answer 7

This code looks like it will loop until it gets studentGrades.length values, no matter what, and if the while loop repeats, it will repeat forever because g is not reinitialized.

I assume this must be a homework problem, so I'll leave the actual coding to fix the bug to you as an exercise.