C Programming - Const - Discussion

I can't understand the concept..

Please explain this.

Please anybody explain this one.

const pointer cannot be passed to non-const parameter.

In line :fun(&ptr);
ptr in non-const, but argument required is const **ptr .

Can Anyone Explain?

Ravi already said it.

Ptr is a const pointer. The argument of fun should be const too.

#include<stdio.h>
int fun(int **ptr);

int main()
{
int i=10;
const int *ptr = &i;{{Probably CONST INT*PTR IS ASSIGNED TO REFERENCE OF 'I' WHICH CNT BE ALTERED BUT PTR IN FUTURE CAN BE ASSIGNED SOMETHING ELSE WHICH WILL NOT GIVE AN ERROR.
const int *ptr = &i;
*PTR=12;//ERROR
ptr=10;//NO ERROR

const int *ptr = &i;
int fun(int **ptr)
{
int j = 223;
int *temp = &j;
printf("Before changing ptr = %5x\n", *ptr);
const *ptr = temp;// HERE IS THE ERROR
printf("After changing ptr = %5x\n", *ptr);
return 0;
}
}

The ptr is declared twice in the function. How come that is not an error?

Ravi explanation is correct.

ptr is not a constant pointer but the value it points to is constant.
ptr is constant pointer, if it should declare like this
int * const ptr;
But it is declared like
const int *ptr;
ptr may points to some other location but the fact here is that it should contain value 10. however in question value changes to 223. that's why error is there.