Javascript: for-loop not working

Question

I have this code right here.. where the variable num is the dimension of a n by n square table. The objective is to enter a number and create a table with the number as the dimension.

I got this code but it doesn't go through the 2 layers of for-loops. After the code execution, the string *change_text* just becomes: <table></table>

    change_text = "<table>";

    for (var i; i<num; i++) {
        change_text = change_text + "<tr>";
        for (var j; j<num; j++) {
            change_text = change_text + "<td> asdf </td>";

            //code for blue cells
        }
        change_text = change_text + "</tr>";
    }


    change_text = change_text+ "</table>"

For reference, you can simply do change_text += "new text"; instead of change_text = change_text + "new text"; — James Donnelly
– James Donnelly, Commented Feb 19, 2013 at 15:00

Joe · Accepted Answer · 2013-02-19 14:44:51Z

8

You need to initialize your iterators:

for(var i = 0; i < num; i++)

answered Feb 19, 2013 at 14:44

Joe

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Comments

Jordan Casey · Accepted Answer · 2018-09-10 22:15:05Z

4

Ohhh also I noticed that num isn't defined specifically. Wherever you're getting num from make sure to use parseInt if it could have possibly been passed as a string.num = parseInt(num);

answered Sep 10, 2018 at 22:15

Jordan Casey

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Comments

Lloyd · Accepted Answer · 2013-02-19 14:44:41Z

2

You need to specify the starting value for your loops:

change_text = "<table>";

    for (var i = 0; i<num; i++) {
        change_text = change_text + "<tr>";
        for (var j = 0; j<num; j++) {
            change_text = change_text + "<td> asdf </td>";

            //code for blue cells
        }
        change_text = change_text + "</tr>";
    }


    change_text = change_text+ "</table>"

At present I would assume i and j are undefined and so the loops won't go anywhere.

answered Feb 19, 2013 at 14:44

Lloyd

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Comments

ddev · Accepted Answer · 2013-02-19 14:44:49Z

2

you need to initialize i and j... try this:

change_text = "<table>";

for (var i=0; i<num; i++) {
    change_text = change_text + "<tr>";
    for (var j=0; j<num; j++) {
        change_text = change_text + "<td> asdf </td>";

        //code for blue cells
    }
    change_text = change_text + "</tr>";
}


change_text = change_text+ "</table>"

answered Feb 19, 2013 at 14:44

ddev

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Comments

zs2020 · Accepted Answer · 2013-02-19 14:44:53Z

2

You need to initialize i and j, like this:

for (var i = 0; i<num; i++)

answered Feb 19, 2013 at 14:44

zs2020

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Comments

sasi · Accepted Answer · 2013-02-19 14:44:58Z

2

Not initialized i,make i=0

 for (var i=0; i<num; i++) {
       //code
    }

answered Feb 19, 2013 at 14:44

sasi

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Comments

Bergi · Accepted Answer · 2013-02-19 14:44:53Z

1

You forgot the i=0/j=0 initialisation. You only declared the variables, and undefined always yields false from numeric comparisons which breaks the loop immediately. So change your code to

change_text = "<table>";
for (var i=0; i<num; i++) {
    change_text = change_text + "<tr>";
    for (var j=0; j<num; j++) {
        change_text = change_text + "<td> asdf </td>";
        //code for blue cells
    }
    change_text = change_text + "</tr>";
}
change_text = change_text+ "</table>"

answered Feb 19, 2013 at 14:44

Bergi

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