In my previous post,<\/a> I began exploring the field of computer science with a look at a for loop. The loop was written in perl. Now I will explain, line by line, the meaning of the loop code:<\/p>\n for ($i=0;$i<3;$i++){<\/span><\/p>\n print “The counter is now at $i.\\n”;<\/span><\/p>\n }<\/span><\/p>\n First off, the dollar sign in front of the i means that i is a variable. In perl, a variable has a dollar sign in front of it to show it’s a variable. Programmers often call a counter variable i, j, or k. So $i<\/span> means “the counter variable i”.<\/p>\n $i<3<\/span> means that as long as the value of i is less than three, the loop will continue running. When i equals 3, the program will exit the loop.<\/p>\n $i++<\/span> means that every time the program executes the loop, it adds 1 to the counter variable (also known as incrementing<\/em> the counter variable by 1). Importantly, a for loop increments the counter variable at the end, rather than at the start.<\/p>\n The brace {<\/span> means the program is entering the loop body, which contains the commands to be executed during each pass through the loop (also known as each iteration<\/em> of the loop). In our case, there is only one instruction:<\/p>\n print “The counter is now at $i.\\n”;<\/span><\/p>\n print<\/span> means display what’s in the quotation marks. The $i<\/span> is displayed as its value each time. Substituting the value of a variable in a quoted sentence is called interpolation<\/em>. The \\n<\/span> means “newline”.<\/p>\n Now, the program reaches the closing brace }<\/span>, which means the loop instructions are complete for this cycle. It’s time to increment the counter and return to the beginning of the loop. If $i<3<\/span>, the loop will execute again.<\/p>\n Hence the output<\/p>\n The counter is now at 0. Hope this clarifies the perl for loop. In a coming post I’ll mention how to get (or find) perl on your own system, should you want to experiment with the code yourself:)<\/p>\n
\nThe counter is now at 1.
\nThe counter is now at 2.<\/p>\n