Javascript: for-loop not working

Question

I have this code right here.. where the variable num is the dimension of an 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>"

Answer 1

您需要初始化您的迭代器：

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

Answer 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.

Answer 3

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>"

Answer 4

您需要初始化 i 和 j，如下所示：

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

Answer 5

Not initialized i,make i=0

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

Answer 6

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);

Answer 7

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>"