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In this Javascript code, why are 2 for loops needed? could you please explain this to...

In this Javascript code, why are 2 for loops needed?

could you please explain this to me.

This is the outcome

*
**
***
****
*****
******
*******
********
*********

the code is

<html>
<head>
      
       <title></title>
      
<script>
      
      
   showStars(10);
      
       function showStars(rows){
           for(var i = 0; i < rows; i++){
               var pattern = "";
               for(var j = 0; j < i; j++)
                   pattern = pattern + "*";
           document.writeln(pattern);
           document.writeln("<br/>");
           }
       }
      
              
</script>
</head>

<body>
      
</body>
</html>

engineering   Computer-Science   
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Answer #1

The first for loop is for the row count.

And the second for loop is to generate the number of stars in that specific row.

Dry run the code:-

when i = 0

i = 0, j = 0

loop condition false as j == i, second loop exit. So loop did not generated any pattern.


when i =1

i =1, j = 0

pattern becomes "*"

i =1, j= 1

loop condition false as j == i, second loop exit

then the pattern = “*” is printed

and the line is changed.


when i = 2

i =2, j = 0

pattern = "*"

i =2, j = 1

pattern = "**"

i =2, j = 2

loop condition false as j == i, second loop exit

printed pattern "**"

changed line


when i = 3

i =3, j = 0

pattern = "*"

i =3, j = 1

pattern = "**"

i =3, j = 2

pattern = "***"

i =3, j = 3

loop condition false as j == i, second loop exit

printed pattern "***"

changed line

and so on...


The first(outer) loop keeps check on the row number and also printing the pattern and changing line for the next pattern to be printed. This loop also reset the pattern variable for the next pattern.

And the second(inner) loop is generating pattern, by checking the loop condition and if it is true. variable pattern is appended with a "*" in it.



function showStars(rows){

           for(var i = 0; i < rows; i++){ // run row times from 0 to row-1

               var pattern = ""; //resetting the pattern

               for(var j = 0; j < i; j++) //generate the pattern, will run from 0 till i-1

                   pattern = pattern + "*"; //appending the pattern with "*"

           document.writeln(pattern); //printing the pattern when the inner loop is terminated

           document.writeln("<br/>"); //change the line for the next pattern to be printed.

           } //first(outer) loop end

       }

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