Computer Programming 简明教程

Computer Programming - Characters

如果在计算机编程中处理数字很简单，那么处理字符将会更简单。字符就像 a、b、c、d……、A、B、C、D……，但有一个例外。在计算机编程中，任何个位数数字，如 0、1、2……和特殊字符，如 $、%、+、- ……等，也都视为字符，要将它们分配给字符类型变量，你只需将其放入 single quotes 中。例如，以下语句定义了一个字符类型变量 ch ，我们给它分配一个值 'a'−

If it was easy to work with numbers in computer programming, it would be even easier to work with characters. Characters are simple alphabets like a, b, c, d…., A, B, C, D,….., but with an exception. In computer programming, any single digit number like 0, 1, 2,….and special characters like $, %, +, -…. etc., are also treated as characters and to assign them in a character type variable, you simply need to put them inside single quotes. For example, the following statement defines a character type variable ch and we assign a value 'a' to it −

char ch = 'a';

在此， ch 是字符类型变量，可以容纳一个实现字符集中的字符，而 'a' 称为 character literal 或字符常量。不仅仅是 a、b、c……，当像 1、2、3……这样的任何数字，或像 !、@、、、$……这样的任何特殊字符保存在单引号内时，它们将被视为字符字面量，可以分配给字符类型的变量，因此以下是一个有效的语句 −

Here, ch is a variable of character type which can hold a character of the implementation’s character set and 'a' is called a character literal or a character constant. Not only a, b, c,…. but when any number like 1, 2, 3…. or any special character like !, @, #, #, $,…. is kept inside single quotes, then they will be treated as a character literal and can be assigned to a variable of character type, so the following is a valid statement −

char ch = '1';

字符数据类型消耗 8 位内存，这意味着您可以将 ASCII 值介于 -127 至 127 之间的内容存储在字符中，因此它可以容纳 256 个不同值中的任何一个。字符数据类型可以存储键盘上的任何字符，包括特殊字符，如 !、@、、、$、%、^、&、*、(、)、_、+、{、} 等。

A character data type consumes 8 bits of memory which means you can store anything in a character whose ASCII value lies in between -127 to 127, so it can hold any of the 256 different values. A character data type can store any of the characters available on your keyboard including special characters like !, @, #, #, $, %, ^, &, *, (, ), _, +, {, }, etc.

请注意，您只能在单引号内保留一个字母或一个数字，且不允许在单引号内有多个字母或数字。因此，以下语句在 C 编程中无效 −

Note that you can keep only a single alphabet or a single digit number inside single quotes and more than one alphabets or digits are not allowed inside single quotes. So the following statements are invalid in C programming −

char ch1 = 'ab';
char ch2 = '10';

下面是一个简单的示例，展示如何在 C 编程语言中定义、分配和打印字符 −

Given below is a simple example, which shows how to define, assign, and print characters in C Programming language −

#include <stdio.h>

int main() {
   char  ch1;
   char  ch2;
   char  ch3;
   char  ch4;

   ch1 = 'a';
   ch2 = '1';
   ch3 = '$';
   ch4 = '+';

   printf( "ch1: %c\n", ch1);
   printf( "ch2: %c\n", ch2);
   printf( "ch3: %c\n", ch3);
   printf( "ch4: %c\n", ch4);
}

在此，我们使用 %c 来打印字符数据类型。当执行上述程序时，它将产生以下结果 −

Here, we used %c to print a character data type. When the above program is executed, it produces the following result −

ch1: a
ch2: 1
ch3: $
ch4: +

Escape Sequences

许多编程语言支持一个称为 Escape Sequence 的概念。当一个字符前带有反斜杠 (\)，它称为转义序列，并且它对编译器具有特殊含义。例如，以下语句中的 \n 是一个有效字符，并且称为换行符 −

Many programming languages support a concept called Escape Sequence. When a character is preceded by a backslash (\), it is called an escape sequence and it has a special meaning to the compiler. For example, \n in the following statement is a valid character and it is called a new line character −

char ch = '\n';

在此，字符 n 前面带有一个反斜杠 (\)，它具有特殊含义，即换行符，但请记住反斜杠 (\) 仅对几个字符具有特殊含义。以下语句在 C 编程中没有任何意义，并且将被认为是一个无效的语句 −

Here, character n has been preceded by a backslash (\), it has special meaning which is a new line but keep in mind that backslash (\) has special meaning with a few characters only. The following statement will not convey any meaning in C programming and it will be assumed as an invalid statement −

char ch = '\1';

下表列出了 C 编程语言中可用的转义序列 −

The following table lists the escape sequences available in C programming language −

Escape Sequence

Description

Inserts a tab in the text at this point.

Inserts a backspace in the text at this point.

Inserts a newline in the text at this point.

Inserts a carriage return in the text at this point.

Inserts a form feed in the text at this point.

Inserts a single quote character in the text at this point.

Inserts a double quote character in the text at this point.

以下示例演示了编译器如何在 print 语句中解释转义序列 −

The following example shows how the compiler interprets an escape sequence in a print statement −

#include <stdio.h>

int main() {
   char  ch1;
   char  ch2;
   char  ch3;
   char  ch4;

   ch1 = '\t';
   ch2 = '\n';

   printf( "Test for tabspace %c and a newline %c will start here", ch1, ch2);
}

当执行上述程序时，它将生成以下结果 −

When the above program is executed, it produces the following result −

Test for tabspace     and a newline
will start here

Characters in Java

以下是用 Java 编写的等效程序。Java 处理字符数据类型的方式与我们在 C 编程中看到的很相似。但是，Java 为字符处理提供了额外的支持。

Following is the equivalent program written in Java. Java handles character data types much in the same way as we have seen in C programming. However, Java provides additional support for character manipulation.

您可以尝试执行以下程序以查看输出，其必须与上述 C 示例生成的输出相同。

You can try to execute the following program to see the output, which must be identical to the result generated by the above C example.

public class DemoJava {
   public static void main(String []args) {
      char  ch1;
      char  ch2;
      char  ch3;
      char  ch4;

      ch1 = 'a';
      ch2 = '1';
      ch3 = '$';
      ch4 = '+';

      System.out.format( "ch1: %c\n", ch1);
      System.out.format( "ch2: %c\n", ch2);
      System.out.format( "ch3: %c\n", ch3);
      System.out.format( "ch4: %c\n", ch4);
   }
}

当执行上述程序时，它将生成以下结果 −

When the above program is executed, it produces the following result −

ch1:  a
ch2:  1
ch3:  $
ch4:  +

Java 也以你在 C 编程中使用它们的方式支持转义序列。

Java also supports escape sequence in the same way you have used them in C programming.

Characters in Python

Python 不支持任何字符数据类型，但所有字符都被视为字符串，它是字符序列。我们将在单独的章节中学习字符串。在 Python 中使用单个字符时，您不需要做出任何特殊安排。

Python does not support any character data type but all the characters are treated as string, which is a sequence of characters. We will study strings in a separate chapter. You do not need to have any special arrangement while using a single character in Python.

以下是使用 Python 编写的等效程序−

Following is the equivalent program written in Python −

ch1 = 'a';
ch2 = '1';
ch3 = '$';
ch4 = '+';

print "ch1: ", ch1
print "ch2: ", ch2
print "ch3: ", ch3
print "ch4: ", ch4

当执行上述程序时，它将生成以下结果 −

When the above program is executed, it produces the following result −

ch1:  a
ch2:  1
ch3:  $
ch4:  +

Python 以你在 C 编程中使用它们的方式支持转义序列。

Python supports escape sequences in the same way as you have used them in C programming.