答案

#include <iostream>
using namespace std;
int main() {
int N;
cin >> N;
N=(N-1)*2+1;
int m= (N + 1) / 2;
for (int i = 1; i <= (N-1)/2; i++) {
for (int j = 1; j <= N; j++) {
if(j-1m-i || j+1m+i){
cout<<'+';
}
else{
cout<<'.';
}
}
cout<<endl;
}
for (int i = (N-1)/2+1; i >=1 ; i--) {
for (int j = 1; j <=N; j++) {
if(j-1m-i || j+1m+i){
cout<<'+';
}
else{
cout<<'.';
}
}
cout<<endl;
}
return 0;
}