\u7c21\u5358\u306a\u554f\u984c\u30021\u304b\u3089n\u307e\u3067\u5408\u8a08\u3092\u8a08\u7b97\u3059\u308b\u30d7\u30ed\u30b0\u30e9\u30e0\u3092\u4f5c\u6210\u3002
\n
\nsum0\u306f\u666e\u901a\u306bfor\u6587\u3092\u4f7f\u3063\u3066\u8a08\u7b97\u3002sum1\u306f\u516c\u5f0f\u3092\u4f7f\u3063\u3066\u8a08\u7b97\u3002n\u304bn+1\u306e\u3069\u3061\u3089\u304b\u304c2\u306e\u500d\u6570\u306b\u306a\u308b\u306e\u3067\u5fc5\u305a\u5272\u308a\u304d\u308c\u308b\u306e\u3067\u3059\u304c\u3001(n+1)*n\/2\u3068\u3059\u308b\u3068double\u578b\u306b\u306a\u308b\u306e\u3067DartEditor\u304c\u8b66\u544a\u3092\u51fa\u3057\u307e\u3059\u3002\u3068\u3044\u3046\u3053\u3068\u3067\u3001double.toInt()\u3092\u547c\u3073\u51fa\u3057\u3066\u3044\u307e\u3059\u3002sum2\u306f\u518d\u5e30\u7684\u547c\u3073\u51fa\u3057\u3002<\/p>\n
\r\nint sum0(int n) {\r\n int sum = 0;\r\n for (int i=1 ; i<=n ; i++) {\r\n sum += i;\r\n }\r\n return sum;\r\n}\r\nint sum1(int n) {\r\n return ((1+n)*n\/2).toInt(); \/\/ double\u306b\u306a\u308b\u306e\u3067toInt()\r\n}\r\nint sum2(int n) {\r\n if (n == 0) {\r\n return 0;\r\n } else {\r\n return sum2(n-1) + n;\r\n }\r\n}\r\n\r\nvoid main() {\r\n print("sum0(10):" + sum0(10));\r\n print("sum1(10):" + sum1(10));\r\n print("sum2(10):" + sum2(10));\r\n}\r\n<\/pre>\n