View Compilation Error

0_0_21363943_13710.cpp: In function 'int main()':
0_0_21363943_13710.cpp:52:4: error: 'res' was not declared in this scope
    res = 0;
    ^
0_0_21363943_13710.cpp:57:5: error: 'res' was not declared in this scope
     res ^= (n * (n + 1) / 2) & 1;
     ^
0_0_21363943_13710.cpp:61:18: error: 'res' was not declared in this scope
   printf("%s\n", res ? "NO" : "YES");
                  ^