Language: C++

#include <iostream>

using namespace std;

int main() {

	int r = 0;

????????????cin >> r;
	
	cout << r * 3.141592653589793238 << endl;

	return 0;

}

Compiler output:
a.cc: In function 'int main()':
a.cc:9:1: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      | ^
a.cc:9:2: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |  ^
a.cc:9:3: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |   ^
a.cc:9:4: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |    ^
a.cc:9:5: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |     ^
a.cc:9:6: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |      ^
a.cc:9:7: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |       ^
a.cc:9:8: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |        ^
a.cc:9:9: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |         ^
a.cc:9:10: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |          ^
a.cc:9:11: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |           ^
a.cc:9:12: error: expected primary-expression before '?' token
    9 | ????????????cin >> r;
      |            ^
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token
a.cc:9:21: error: expected ':' before ';' token
    9 | ????????????cin >> r;
      |                     ^
      |                     :
a.cc:9:21: error: expected primary-expression before ';' token