C Programming

Question

What is the o/p of following code?

#include  <stdio.h>

int main(void)
{
    int arr[5]={1,2,3,4,5};
    int i;
    for(i=2;i<=5;i++)
    printf("%d ",arr[i*10]);
    return 0;
}

Comments

Dummy numbers will be printed...

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why this code does not give compile time error.

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I think this Program is Compiler Dependent.

1:Codechef Online Compiler : Prints Garbage Values.

2. TutorialS Point Online Compiler : Prints all Zeroes. 0 0 0 0

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what is the role of this code:  printf("%d ",arr[i*10]);

what is the meaning of arr[i*10]???

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• printf("%d ",arr[i*10]);

Here in arr[i*10] means address: arr[0] + 10 units  for i=1;

            arr[i*10] means address: arr[0] + 20  units for i=2; and so on.

Note : That simply shows array index out of bound.... That's the reason why this lines are compiler dependent and shows undefined behavior. 

Because some compilers shows it as Garbage Values and the Rest gives 0.

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Because syntax of given program code is true,

But there is problem with array bound that is for i=2 arr[i * 10]  is arr[20]

Size of arr is 5 so it can be perform operation in the range arr[0] to arr[5]

element arr[20] is not bound that is this element is out of bound hence it gives the garbage value

Answer 1

o/p : Undefined Behavior i mean some random values (garbage)

Actually it won't generate segmentation fault because C don't check array bounds to make their work fast.

Bound checking would make the execution slower think one time like every time you access an element of array , compiler performs whether this element is out of bound or not . C don't do this for optimization purpose.

Comments

Thanks

Answer 2

I think this Program is Compiler Dependent.

1:Codechef Online Compiler : Prints Garbage Values.

2. TutorialS Point Online Compiler : Prints all Zeroes. 0 0 0 0