for 循環

for(初始條件；比較；狀態改變  )
｛
 循環體
 ｝
 打印100遍helloword
for(int i=0;i<100,i++)
{
 console.writeline("helloword");
 }
求1-100的和
 int s = 0;
for(int i=1;i<=100;i++)
 {
  s = s + i;
 }
 Console.WriteLine(s);
 Console.ReadLine();
100之內全部與7相關的數和，奇數和，偶數和
int s = 0;
for (int i = 1; i <= 100; i++)
{
 if ((i%7==0)||(i%10==7)||(i/10 ==7))
{
s = s + i;
}
}
Console.WriteLine(s);
 Console.ReadLine();
100之內的全部質數和
int sum = 0;
for (int i=2;i<=100;i++)
{
 int a = 0;
for (int j = 1; j <=i; j++)
if (i % j == 0)//若是i能被它自己和1之外的數整除，那麼他就不是質數
{
a++;
 }
 }
if (a == 2)  //能被整除的數只有兩個，即爲質數
 {
  sum = sum + i;
  }
  }
 Console.Write(sum);
 Console.ReadLine();
打印☆，排列成圖形
右上
for (int m=1;m <10;m++)
 {
 for(int n=1;n<=m;n++)
 {
  Console.Write("☆");
 }
 Console.Write("\n");
}           
右下
 for (int m = 10; m > 1; m--)
 {
  for (int n = 1; n < m; n++)
 {
   Console.Write("☆");
 }
   Console.Write("\n");
 }
左下
for (int m = 1; m < 10; m++)
{
 for (int n = 1; n < m; n++)
{
 Console.Write("  ");
}
for (int l = 10; l > m; l--)
{
 Console.Write("☆");
 }
 Console.Write("\n");
 }
左上
for (int m = 1; m < 10; m++)
{
for (int n = 9; n >m; n--)
{
Console.Write("  ");
}
for (int l = 1; l <= m;l++ )
{
 Console.Write("☆");
 Console.Write("\n");
 }  
上半部分
for (int m = 1; m < 10; m++)
{
for (int n = 9; n > m; n--)
{
Console.Write("  ");
}
for (int l = 1; l <= (2 * m - 1); l++)
{
 Console.Write("☆");
}
Console.Write("\n");
}
下半部分
for (int m = 1; m < 9; m++)
{
 for (int l = 1; l <= m; l++)
{
 Console.Write("  ");
}
 for (int n = 1; n <= (2 * (9 - m) - 1); n++)
{
 Console.Write("☆");
}
 Console.Write("\n");
}
一對幼兔一個月後長成小兔，再過一個月長成成兔並生下一對小兔，兩年後有多少對兔子？
int a = 1, b = 0, c = 0;
for (int i = 2; i <= 24; i++)
{
 if (i == 1)
{
c = 0;
b = 0;
a = 1;
}
else
{
c = c + b;
b = a;
a = c;
}
Console.WriteLine("第{0}個月,成兔數量:{1}小兔數量{2}:幼兔數量{3}", i, c, b, a);
 Console.ReadLine();
}
Console.WriteLine("總數量爲" + (c + a + b));
Console.ReadLine();
窮舉問題：鉛筆一支2元，筆盒5元，文件夾10元，彩筆5元，買正好100塊的文具，每種至少買一種，
列舉出全部方法
for (int qianbi = 1; qianbi <= 50; qianbi++)
{
 for (int he = 1; he <= 20; he++)
{
 for (int wenjianjia = 1; wenjianjia <= 10; wenjianjia++)
{
 for (int caibi = 1; caibi <= 7; caibi++)
{
 int a = qianbi * 2 + he * 5 + wenjianjia * 10 + caibi * 15;
 if (a == 100)
{
Console.WriteLine("鉛筆買{0}只,盒買{1}個,文件夾買{2}個,彩筆買{3}支",
qianbi, he, wenjianjia, caibi);
}
}
}
}
}
Console.ReadLine();