Using for loop after if /else statement

Question

This is just a simple multiplication program using an if / else and for loop. Re - entering a positive number from a prompt and assigning it to the num variable which the for loop should use is breaking the program.I’ m not sure why it is incorrect. ? Perhaps you could tell me the best way to do this using the if / else and for loop. Any help much appreciated.

//Array variable and counter variable

var multi = new Array();

var Counter;

//Enter a number between 1 and 12 and hold in num variable

num = prompt("Enter a number between 1 and 12");

//Check if number is less than zero
//Reenter positive number

if (num < 0) {
    var num = prompt("Enter a number greater than zero");
} 
else {
    //Number entered by user multiplied by counter value
    for (Counter = 1; Counter <= 12; Counter++) {
        multi[Counter] = num * Counter;
    }
    //Loop to display number that is being multiplied each time 
    for (Counter = 1; Counter <= 12; Counter++) {
        document.write(Counter + " x " + num + "  = " + multi[Counter] + '<br/>');
    }
}

It should be var num instead of num and then num instead of var num. — Sebastian Simon
– Sebastian Simon, Commented Oct 10, 2015 at 14:41
why are you using two diff loops you multiply and display in one for loop right? — Tummala Krishna Kishore
– Tummala Krishna Kishore, Commented Oct 10, 2015 at 14:42
var num; do { num = prompt("Enter a number between 1 and 12"); } while (num < 1 || num > 12); — melpomene
– melpomene, Commented Oct 10, 2015 at 14:42
What does "breaking the program" mean, what exactly doesn't work ? — adeneo
– adeneo, Commented Oct 10, 2015 at 14:44

joshfarrant · Accepted Answer · 2015-10-10 14:54:48Z

1

This can be simplified at the same time as fixing your code.

The reason entering a negative number was causing the code to fail was because you would never hit the else block and so never run the intended code within it.

As suggested by melpomene a do/while loop will serve you well here.

You also don't need 2 separate for loops, they can be condensed into one.

var num;

do {

  // Enter a number between 1 and 12 and hold in num variable
  // Check if number is not between 1 and 12 and re-enter
  num = prompt("Enter a number between 1 and 12");

} while (num < 1 || num > 12);

// You can define your counter variable within the for loop
for (var counter = 1; counter <= 12; counter++) {

   document.write(counter + ' x ' + num + '  = ' + (num * counter) + '<br/>')

}

edited Oct 10, 2015 at 14:54

answered Oct 10, 2015 at 14:49

joshfarrant

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2 Comments

Jack Reacher Over a year ago

Thank you very much Josh. I didn't realise I was never hitting the else block. I spent a lot of time on this, pitfalls of being a new programmer.

joshfarrant Over a year ago

No problem - keep at it!

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