Questions

1. What is difference between For loop and While loop ?
    
The while loop is usually used when you need to repeat something until a given condition is true:

inputInvalid = true;
while(inputInvalid)
{
    //ask user for input
    invalidInput = checkValidInput();
}

On the other hand, the for loop is usually used when you need to iterate a given number of times:

for(var i = 0; i < 100; i++)
{
    ...//do something for a 100 times.
}