Main.cc: In function 'int main()': Main.cc:10:5: error: expected ';' before 'for' for(int i=3;i<=n;i++){ ^ Main.cc:10:17: error: 'i' was not declared in this scope for(int i=3;i<=n;i++){ ^ Main.cc:8:15: warning: unused variable 'j' [-Wunused-variable] int n,a=1,j=1; ^