Nested if/else in While loop

Question

I'm trying to make a program that determines if a grade entered is passing or failing. It stops when the user enters -1. Once the user does enter -1, it has to print out the average of the passing scores and the total amount of scores. It's not really working correctly though. What am I doing wrong?

var countTotal=0;   //variable to store total grades.
var countPassing=0; //variable to store total passing scores.
var x= 0;       //variable to contain sum of all passing scores.
var grade=parseInt(prompt("Please enter a grade."));

while (grade != (-1*1)) 
{
    if (grade > 65) {
        grade=parseInt(prompt("Please enter a grade."));
        document.write(grade + " is passing.<br>");
        x=x+grade;
        countPassing++;
    }
    else {
        grade=parseInt(prompt("Please enter a grade."));
        document.write(grade + " is failing.<br>");
    }

    countTotal++;
}

//Loop ends

document.write("Total # of grades: " + countTotal);         //Prints out total # of passing scores.
document.write("Passing average: " + ((x)/(countPassing))); //Prints out average of all passing scores.

Just to satisfy my curiousity ... what is the point of (grade != (-1*1))? Shouldn't (grade != -1) be sufficient? — Joel Etherton
– Joel Etherton, Commented Nov 14, 2012 at 15:04
yeah you're absolutely right, but I just wanted to make sure that it would work as an integer. Im quite new to this haha — user1765804
– user1765804, Commented Nov 14, 2012 at 15:08
@user1765804: That's quite alright, I just wanted to point it out. As a note, parseInt should take care of that for you. — Joel Etherton
– Joel Etherton, Commented Nov 14, 2012 at 15:10
It's important to pass in the radix argument to parseInt: parseInt(grade, 10). Otherwise, if you get something that starts with a 0, it will be interperted as octal. — user20416
– user20416, Commented Nov 14, 2012 at 15:10

Tayacan · Accepted Answer · 2012-11-14 15:03:44Z

1

Try working through it by hand. The user enters the very first grade. Then the loop starts. Immediately, you ask for a new grade, discarding the first one. If you move the prompt down to the end of the loop, it should work. Like this:

while (grade != (-1*1)) 
{
    if (grade > 65) {
        document.write(grade + " is passing.<br>");
        x=x+grade;
        countPassing++;
    }
    else {
        document.write(grade + " is failing.<br>");
    }

    grade=parseInt(prompt("Please enter a grade."));
    countTotal++;
}

answered Nov 14, 2012 at 15:03

Tayacan

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2 Comments

user1765804 Over a year ago

oh ok, that makes sense. For the life of me, I could not figure out why it would do that. It actually seemed to be discarding the second value entered, but this works. Thanks.

Tayacan Over a year ago

Hmm. I tested it, and it discarded the first one. For some reason, the average was wrong too before I changed it, but it seems to work now.

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