---

Lỗi biên dịch:

Main.cc: In function ‘int main()’:
Main.cc:9:26: warning: for increment expression has no effect [-Wunused-value]
     for (int i=3; i<=n; i+2) {
                         ~^~
Main.cc:13:9: error: expected ‘;’ before ‘else’
         else if (c == '-')
         ^~~~
Main.cc:16:5: error: expected ‘;’ before ‘}’ token
     }
     ^
Main.cc:7:10: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ~~~~~^~~~~~~~~~