foo.cpp: In function 'int main()':
foo.cpp:16:21: error: 'n' was not declared in this scope
  scanf("%d%d%d%d", &n, &m, &k, &x);
                     ^
foo.cpp:16:25: error: 'm' was not declared in this scope
  scanf("%d%d%d%d", &n, &m, &k, &x);
                         ^
foo.cpp:16:29: error: 'k' was not declared in this scope
  scanf("%d%d%d%d", &n, &m, &k, &x);
                             ^
foo.cpp:16:33: error: 'x' was not declared in this scope
  scanf("%d%d%d%d", &n, &m, &k, &x);
                                 ^