3.6 Conditionals 条件语句

The way statements are sequenced and combined in a program determines the computed result. Programs incorporate iteration and selection constructs to represent repetition and make decisions to handle varied input values.

• 程序中语句的排序和组合方式决定了计算结果。程序结合迭代和选择结构来表示重复并做出决策来处理各种输入值。

核心要点 Core Points

1. Selection determines which parts of an algorithm are executed based on a condition being true or false.

   • 选择根据条件为真或假来确定算法的哪些部分被执行。

2. Conditional statements, or "if-statements," affect the sequential flow of control by executing different statements based on the value of a Boolean expression.

   • 条件语句或"if语句"通过根据布尔表达式的值执行不同的语句来影响控制的顺序流。

3. The exam reference sheet provides the following syntax for conditional statements:

   • 考试参考表提供以下条件语句语法：
   • Text:
     • 文本：

     IF (condition)
     {
       <block of statements>
     }

   • Block:
     • 块：

     IF (condition)
     [block of statements]

4. The exam reference sheet provides the following syntax for IF-ELSE conditional statements:

   • 考试参考表提供以下IF-ELSE条件语句语法：
   • Text:
     • 文本：

     IF (condition)
     {
       <first block of statements>
     }
     ELSE
     {
       <second block of statements>
     }

   • Block: A visual representation showing the IF-ELSE structure
     • 块： 显示IF-ELSE结构的视觉表示

5. In an IF statement, the code in block of statements is executed if the Boolean expression condition evaluates to true; no action is taken if condition evaluates to false.

   • 在IF语句中，如果布尔表达式条件计算为真，则执行语句块中的代码；如果条件计算为假，则不采取任何行动。

6. In an IF-ELSE statement, the code in first block of statements is executed if the Boolean expression condition evaluates to true; otherwise, the code in second block of statements is executed.

   • 在IF-ELSE语句中，如果布尔表达式条件计算为真，则执行第一个语句块中的代码；否则，执行第二个语句块中的代码。

学生活动 Student Activities

1. Express an algorithm that uses selection without using a programming language.

   • 表达一个使用选择而不使用编程语言的算法。

2. For selection:

   • 对于选择：
   • Write conditional statements.
     • 编写条件语句。
   • Determine the result of conditional statements.
     • 确定条件语句的结果。

相关资源 Related Resources

• Professional Development > Teaching and Assessing: Algorithmic Thinking from College Board

  • 专业发展 > 教学与评估：算法思维 来自大学理事会

• AP CSP Exam Reference Sheet

  • AP CSP考试参考表