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#include <iostream>
using namespace std;
 
int main() {
	// your code goes here
	int arr[]={1,2,3,4};
	const int *p1 = &arr[0]; // non-const ptr to const data
	int const *p2 = &arr[0]; // non-const ptr to const data
	int* const p3 = &arr[0]; // const ptr to non-const data
	const int* const p4 = &arr[0]; // const ptr to const data
 
	p1++; // ok
	p1[0]++; // compile error: modifying const data
 
	p2++; // ok
	p2[0]++; // compile error: modifying const data
 
	p3++; // compile error: modifying const ptr
	p3[0]++; // ok 
 
	p4++; // compile error: modifying const ptr
	p4[0]++; // compile error: modifying const data
 
	return 0;
}

prog.cpp: In function ‘int main()’:
prog.cpp:13:7: error: increment of read-only location ‘* p1’
  p1[0]++; // compile error: modifying const data
       ^
prog.cpp:16:7: error: increment of read-only location ‘* p2’
  p2[0]++; // compile error: modifying const data
       ^
prog.cpp:18:4: error: increment of read-only variable ‘p3’
  p3++; // compile error: modifying const ptr
    ^
prog.cpp:21:4: error: increment of read-only variable ‘p4’
  p4++; // compile error: modifying const ptr
    ^
prog.cpp:22:7: error: increment of read-only location ‘*(const int*)p4’
  p4[0]++; // compile error: modifying const data
       ^

Standard output is empty