What does ":" mean in C language?

The colon (:) in C language has many uses: as a label colon, marking the location of a code block. In conditional statements, separate condition and statement blocks. Within a loop statement, separate loop initialization, conditional expressions, and statement blocks. In the ternary operator, used to convert a conditional expression into a value. In C, used to specify the scope of a namespace or class. In a bit field, specifies the bit width. Other uses include enumeration declarations, case statements, and preprocessor macros.

The colon (:) in C language

The colon (:) in C language is a special symbol , has different meanings in different contexts.

1. Labels

Colons can be used as labels to mark the location of a block of code so that a goto statement can be used to jump to that location. The syntax is as follows:

<code class="c">label: // 标签名称</code>

2. Conditional statements

In conditional statements (if, else, switch), colons are used to separate conditions and statement blocks. The syntax is as follows:

<code class="c">if (condition) :
  // if 分支语句块
else :
  // else 分支语句块</code>

3. Loop statement

In for, while and do-while loops, colons are used to separate loop initialization, conditional expressions and statement blocks . The syntax is as follows:

<code class="c">for (initialization; condition; increment) :
  // 循环语句块</code>

4. Ternary operator

The colon is part of the ternary operator and is used to convert conditional expressions into values. The syntax is as follows:

<code class="c">(condition) ? true_value : false_value</code>

5. Scope operator

In C, the colon and :: operator combination are used to specify the scope of a namespace or class. The syntax is as follows:

<code class="cpp">namespace_name::class_name;</code>

6. Bit field

The colon is used to specify the bit width of the bit field. The syntax is as follows:

<code class="c">struct {
  unsigned int bit_field : width;
}</code>

7. Other uses

The colon is also used for the following other purposes:

• Separating enumerations in an enumeration declaration Citing constants and values
• Separating case labels and statement blocks in case statements
• Separating macro names and macro bodies in preprocessor macros

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