-1

I searched all over the internet to know what does this means :

while(i++)

I've seen a lot of code similar at this. What does the incrementation return to the condition of the while loop ?

Malik Fassi
  • 488
  • 1
  • 10
  • 25

5 Answers5

1

The construct i++ does two things. It evaluates to the current value of the variable i, and it then increments the stored value by one. So, if i is equal to -1, then in the case of while(i++), i++ evaluates to -1, which (being nonzero) is true, increments i to 0, the the loop body is executed, and on the next iteration, i++ evaluates to zero and increments i to 1, and zero being false, the while finishes and execution proceeds beyond it.

This isn't my real name
  • 4,869
  • 3
  • 17
  • 30
  • Thank you ! And can you tell me what does the assignation ? ex : `while(a = b)` My first guess is that it returns the value of b ... Well, I think t could only be that .. – Malik Fassi Jul 25 '13 at 04:44
  • @MalikFassi While(a=b) just assigns values of `b` to `a`. – Rohan Jul 25 '13 at 04:47
  • `while(a=b)` assigns the value of `b` to `a`, and evaluates to that value. This is almost always an error... What's usually meant is `while(a==b)`, which evaluates to true as long as `a` and `b` have the same value. – This isn't my real name Jul 25 '13 at 04:49
  • @MalikFassi If in case you want to compare try `while (a == b)` – 0decimal0 Jul 25 '13 at 04:50
1

The incrementation doesn't return anything to while loop condition.The value of the variable i is first checked to be true a and then it is incremented.

True means anything not equal to 0.

0decimal0
  • 3,884
  • 2
  • 24
  • 39
  • So, the use of i++ to only increment is theoretically false ? As the evaluation is in excess. – Malik Fassi Jul 25 '13 at 04:50
  • it returns.. it just returns the previous value – xaxxon Jul 25 '13 at 04:51
  • @xaxxon OP just intended that this will return the incremented value and I answered according to that :) ... incrementation indeed is done after the condition is evaluated so , its not incrementation which returns :) – 0decimal0 Jul 25 '13 at 04:52
1

In while( i++ ),value of i is evaluated as condition of while, after which i is incremented by 1. This is called as post increment in C which has side-effect.

Example,

i = 1;
while( i++ )    // same as while( i ), 
                // side-effect is `i` incremented by 1 after this 
                // now i is 2

Refer, this question for more information on increment operators.

Community
  • 1
  • 1
VoidPointer
  • 3,037
  • 21
  • 25
1

you can try this code:

  #include"stdio.h"                                                                                                                                                          

  int main()
  {
      int i = -3;
      while(i++)
          printf("NUM I IS: %d\n",i);
      i = -3;
      printf("\n");
      while(++i)
         printf("NUM I IS: %d\n",i);
      return 0;
  }

the result is:

NUM I IS: -2
NUM I IS: -1
NUM I IS: 0

NUM I IS: -2
NUM I IS: -1

See, the second loop run only twice but first loop run 3th.

So

while(i++)

==>

while(i)
{
    i = i +1;
    ...
}

And

while(++i)

==>

while( i = i+1)
Lidong Guo
  • 2,817
  • 2
  • 19
  • 31
0

WHILE loop understands only two things i.e. TRUE and FALSE.

TRUE=any value other than 0

FALSE=0

If the condition is true, the loop will run otherwise, it will get terminated.

In your case, you say WHILE(i++) that means you will keep incrementing the value of i & loop will go on until you get a 0

example:

i= -2;
WHILE(i++)
{
condition
}

In first loop, value of i will be -2 which is true. Condition will be executed & then i will be incremented. Thus, value of i now becomes-2+1 = -1

In second loop, value of i will be -1 which is true. Condition will be executed & then i will be incremented. Thus, value of i now becomes -1+1 = 0

In third loop, value of i will be 0 which is false. Thus loop gets terminated.