CODEWITHSUNDEEP
javamath
Mario
Mario

Reputation: 227

Getting infinity when should be getting percent

Here is the output I'm getting "1 student(s) passed: Infinity" when I should be getting 100% instead of Infinity. Any insight on this issue would be greatly appreciated!

public class PassFailCount {
    public static void main(String[] args) {
        char grade;
        int numFails = 0;
        int numPass = 0;
        float percentFailed;
        float percentPassed;

        do {

            System.out.print("Enter a grade: ");
            grade = 'A';

            if (grade == 'A' || grade == 'B' || grade == 'C' || grade == 'D') {
                numPass++;
            } else {
                numFails++;
            }
            grade = 'Z';

        } while (grade != 'Z');

        percentPassed = (float) numPass * 100 / numFails;
        System.out.println(numPass + " student(s) passed: " + percentPassed);
    }
}

Upvotes: 1

Views: 452

Answers (7)

James Dunn
James Dunn

Reputation: 8274

The reason you are getting Infinity is because you are dividing by 0 with floats (numFails == 0). (If you hadn't cast your division to a float, you would have gotten:
Exception in thread "main" java.lang.ArithmeticException: / by zero!)

What you need to do is divide by the total number of scores, not just the number of failing scores. Like so:

percentPassed = (float) numPass * 100 / (numPass + numFails);

Upvotes: 0

amukhachov
amukhachov

Reputation: 5900

You should divide numPass by numTotal, not numFails. Smth like this:

public class PassFailCount {
public static void main(String[] args) {
    char grade;
    int numTotal = 0;
    int numPass = 0;
    float percentFailed;
    float percentPassed;

    do {

        System.out.print("Enter a grade: ");
        grade = 'A';

        if (grade == 'A' || grade == 'B' || grade == 'C' || grade == 'D') {
            numPass++;
        }
        numTotal++;
        grade = 'Z';

    } while (grade != 'Z');

    if (numTotal != 0) {
        percentPassed = (float) numPass * 100 / numTotal;
    }
    System.out.println(numPass + " student(s) passed: " + percentPassed);
}

}

Upvotes: 0

Atul O Holic
Atul O Holic

Reputation: 6792

You are using wronfg formula for getting the percentage

Instead of ,

 percentPassed = (float) numPass * 100 / numFails;

it should be

 percentPassed = (float) numPass * 100 / totalNumOfStudents;

Also, the issue as rightly pointed is divide by zero which results to infinity.

Upvotes: 0

upog
upog

Reputation: 5531

try

percentPassed = (float) numPass * 100 / (numPass+numFails);

Upvotes: 1

Marko Topolnik
Marko Topolnik

Reputation: 200158

       grade = 'Z';

    } while (grade != 'Z');

You are executing exactly one iteration through your loop. If numFails happens to remain zero after it, division by zero ensues.

Upvotes: 0

Andy Thomas
Andy Thomas

Reputation: 86411

If you want the percentage passed, you need to divide by the total, not the number failed.

float percentPassed = (((float) numPass) / (numPassed + numFailed)) * 100;

Upvotes: 1

Jean Logeart
Jean Logeart

Reputation: 53819

You are dividing a float by zero, which gives infinity.

That is the case when numFails is equal to 0.

Upvotes: 0

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