C语言 用for双重循环 编写一个有9行由*组成的菱形。

以下是使用 C 语言编写一个输出 9 行由星号组成的菱形的程序，使用了双重 for 循环：

```c

#include <stdio.h>

int main() {

int rows = 9

int i, j, k

for (i = 1i <= rowsi++) {

for (j = 1j <= rows - ij++) {

printf(" ")

}

for (k = 1k <= 2 * i - 1k++) {

printf("*")

}

printf("

")

}

for (i = rows - 1i >= 1i--) {

for (j = 1j <= rows - ij++) {

printf(" ")

}

for (k = 1k <= 2 * i - 1k++) {

printf("*")

}

printf("

")

}

return 0

}

```

在上面的代码中，我们首先定义了一个变量 rows，它表示菱形的行数。接着使用了两个 for 循环来产生菱形的上半部分和下半部分。对于每一行，我们使用内层的 for 循环来打印菱形的空格和星号。外层的 for 循环则用于控制总共需要多少行。其中，第一个循环从 1 到 rows，第二个循环从 rows - 1 到 1。这样就可以输出完整的菱形了。

示例输出：

```

*

***

*****

*******

*********

*******

*****

***

*

```

希望这个代码可以帮助你实现你所需的功能

以下是一个求菱形面积的C语言程序：

```c

#include <stdio.h>

int main() {

float diagonal1, diagonal2, area

printf("请输入菱形对角线1的长度：")

scanf("%f", &diagonal1)

printf("请输入菱形对角线2的长度：")

scanf("%f", &diagonal2)

area = (diagonal1 * diagonal2) / 2.0

printf("该菱形面积为：%f\n", area)

return 0

}

```

运行程序后，会提示用户输入两条对角线的长度，然后通过公式计算出菱形面积并输出。其中，变量`diagonal1`和`diagonal2`分别表示两条对角线的长度，变量`area`表示菱形面积。

需要注意的是，在计算过程中要将乘积除以二才能得到正确结果。

for(i=1i<=4i++)

{

这个小的for是打印每一行前边的空格

for(j=1j<=4-ij++)

System.out.print(" ")

这个是打印星星的

for(j=1j<=2*i-1j++)

System.out.print("*")

这个是打印完一行的换行

System.out.println("")

}

下边的是一样的  只不过每一行的空格和星星数   和上边是翻过来的

for(i=1i<=3i++)

{

for(j=1j<=ij++)

System.out.print(" ")

for(j=1j<=7-2*ij++)

System.out.print("*")

System.out.println("")

}

java.sql.SQLException: 无效的列索引

无效的列索引

at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:111)

at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:145)

at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:207)

atoracle.jdbc.driver.OraclePreparedStatement.setStringInternal(OraclePreparedStatement.java:5328)

atoracle.jdbc.driver.OraclePreparedStatement.setString(OraclePreparedStatement.java:5320)

at untitled5.addreader1.validID(addreader1.java:128)

at untitled5.addreader1.jButton1_actionPerformed(addreader1.java:97)

at untitled5.addreader1_jButton1_actionAdapter.actionPerformed(addreader1.java:175)

at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)

at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)

at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)

at javax.swing.DefaultButtonModel.setPressed(Unknown Source)

at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)

at java.awt.Component.processMouseEvent(Unknown Source)

at javax.swing.JComponent.processMouseEvent(Unknown Source)

at java.awt.Component.processEvent(Unknown Source)

at java.awt.Container.processEvent(Unknown Source)

at java.awt.Component.dispatchEventImpl(Unknown Source)

at java.awt.Container.dispatchEventImpl(Unknown Source)

at java.awt.Component.dispatchEvent(Unknown Source)

at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)

at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source

at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)

at java.awt.Container.dispatchEventImpl(Unknown Source)

at java.awt.Window.dispatchEventImpl(Unknown Source)

at java.awt.Component.dispatchEvent(Unknown Source)

at java.awt.EventQueue.dispatchEvent(Unknown Source)

at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)

at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.run(Unknown Source)

代码：String driverName = "oracle.jdbc.OracleDriver"

Driver driver = (Driver) Class.forName(driverName).newInstance()

//连接数据库

Connection con = DriverManager.getConnection(

"jdbc:oracle:thin:@LONG:1521:orcl", "sysman", "tongfang")

PreparedStatement pstmt = con.prepareStatement(

" insert into reader values(?)")

pstmt.setString(1, str1)

pstmt.setString(2,str2)

pstmt.setString(3,str3)

pstmt.setString(4,str4)

ResultSet res = pstmt.executeQuery()

---