Loops (while and for)

Question

In the picture below:

Can anyone explain to me why ‘while’ loop starting from 2 but in the case of ‘for’ loop it is starting from 1 (although i++ is available for both in Program 1 and Program 2) and also in the case of ‘while’ loop the outputs are different in Program 1 and Program 3  but in case of ‘for’ loop the outputs are same although in Program 2 it is post increment (i++) and in Program 4 it is pre increment (++i).

 

Answer 1

In for loop, ++i or i++ is executed after entire loop body is executed. After ++i/i++,  condition is checked if it is true it will execute the loop body else will exit the loop. So it won’t make any diff in program 2 and 4.

But in case of while ++i/i++ is done in the condition itself, so it will follow the pre increment (++i) and post increment (i++)/

Pre increment – ++i → i value will be incremented first then will be used in the expression. So in program 3 it will iterate from 2 to 10 and values printed will be 2 to 10.

Post increment – ++ → i value will be used in the expression then it will be incremented. So in program 4 it will iterate from 1 to 10 but values printed will be 2 to 11.

Answer 2

The property of for loop is that it will execute the i++ part after the execution of the body. But in the while loop i++ part is executing before the body. That’s why you are getting these output.