例如我要输入一个值，那么就会显示相应的三角形
                                                                         N=3  行数为I
                                                                        
例如我输入3 按确定，那么就会出来这么一个三角形                 *        这里就是 （N-I）个‘’+1*2（I-1）* +（N-I）个‘空’
                                                              ***
                                                             *****

如此类推5                                                         *
                                                                 ***
                                                                *****
                                                               *******
                                                              *********
求教怎样做成这样..