C Programming Preprocessor Directives Quiz
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Questions and Answers

Preprocessor directives in C are executed after the program is compiled.

False (B)

Which of the following symbols is used to start a preprocessor directive?

  • *
  • !
  • # (correct)
  • %

    • What is the primary purpose of a macro in C?

    Macro substitution replaces a named code block with its actual definition.

    The #define directive is used to define a _____.

    <p>macro</p> Signup and view all the answers

    Which of the following preprocessor directives allows you to include a header file in your C program?

    <p>#include (C)</p> Signup and view all the answers

    Match the following preprocessor directives with their primary functionalities.

    <p>#define = Macro definition #include = File inclusion #ifdef = Conditional compilation</p> Signup and view all the answers

    In the directive #include <stdio.h>, the angle brackets (<>) indicate that the compiler should search for the file in the ______ directory.

    <p>standard</p> Signup and view all the answers

    A semi-colon (;) is required at the end of a preprocessor directive definition.

    <p>False (B)</p> Signup and view all the answers

    What is the purpose of the #if preprocessor directive?

    <p>To conditionally compile code based on a condition (C)</p> Signup and view all the answers

    The #if directive evaluates an ______ to determine whether to compile the code following it.

    <p>expression</p> Signup and view all the answers

    If the condition specified in the #if directive is false, the code following the #if will be executed.

    <p>False (B)</p> Signup and view all the answers

    The #undef preprocessor directive is used to ____ a constant or macro previously defined by #define.

    <p>undefine</p> Signup and view all the answers

    What does #endif signify in the context of #if directives?

    <p>The end of the <code>#if</code> block.</p> Signup and view all the answers

    The #undef directive defines a preprocessor constant to a limited scope.

    <p>False (B)</p> Signup and view all the answers

    What is the correct syntax for using the #undef preprocessor directive?

    <p>#undef token (C)</p> Signup and view all the answers

    If the #if condition is false, the code inside the ______ block will be executed.

    <p>#else</p> Signup and view all the answers

    What happens when you use #undef on a constant or macro that has not been defined previously?

    <p>It has no effect.</p> Signup and view all the answers

    Which of these preprocessor directives can be used in conjunction with #if to create multiple conditions?

    <p>#elif (A)</p> Signup and view all the answers

    In the provided code snippet, the #if condition is true because the variable a is defined and initialized.

    <p>False (B)</p> Signup and view all the answers

    Match the following preprocessor directives with their respective actions:

    <p><code>#define</code> = Defines a constant or macro <code>#include</code> = Includes a header file <code>#undef</code> = Undefines a constant or macro <code>#ifdef</code> = Checks if a constant is defined <code>#ifndef</code> = Checks if a constant is not defined</p> Signup and view all the answers

    Match the following preprocessor directives with their descriptions:

    <p>#if = Starts a block of code that is conditionally compiled based on an expression #else = Starts a block of code that is executed only if the preceding <code>#if</code> or <code>#elif</code> condition is false #endif = Marks the end of an <code>#if</code> block #elif = Starts a block of code that is executed only if the preceding <code>#if</code> or <code>#elif</code> condition is false and a new expression is true</p> Signup and view all the answers

    In the provided program example, what output will be generated after compilation and execution?

    <p>Value of Number is non-zero (C)</p> Signup and view all the answers

    The #undef directive is used to define the preprocessor constant to a limited scope.

    <p>False (B)</p> Signup and view all the answers

    What is the purpose of the getch() function used in the provided program example?

    <p>The <code>getch()</code> function waits for a key press from the user before ending the program.</p> Signup and view all the answers

    What is the purpose of the #ifdef directive in C?

    <p>It is used to conditionally compile code based on the existence of a macro. (B)</p> Signup and view all the answers

    The #else directive is optional in an #ifdef block.

    <p>True (A)</p> Signup and view all the answers

    What is the output of the following C code snippet?

    #include <stdio.h>
#define X 10

int main() {
  #ifdef X
  printf("one");
  #else
  printf("two");
  #endif
  return 0;
}

    <p>one</p> Signup and view all the answers

    The #endif directive marks the end of a(n) _____ block.

    <p>conditional compilation</p> Signup and view all the answers

    Which of the following C code snippets will output "two"?

    <pre><code class="language-C">#define Y 10 int main() { #ifdef X printf(&quot;one&quot;); #else printf(&quot;two&quot;); #endif return 0; } ``` (A) </code></pre> Signup and view all the answers

    What is the main difference between #ifdef and #ifndef directives in C?

    <p><code>#ifdef</code> checks if a macro is defined, while <code>#ifndef</code> checks if a macro is <em>not</em> defined.</p> Signup and view all the answers

    Conditional compilation can be used to create platform-specific code in C programs.

    <p>True (A)</p> Signup and view all the answers

    Flashcards

    Preprocessor Directives

    Statements processed before compilation in C.

    Macro Processor

    Another name for the C preprocessor.

    Macro Substitution

    Replaces a name with a code snippet using #define.

    File Inclusion

    Directives to include files in a C program.

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    Standard Directory Search

    Using #include <> to find files in standard locations.

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    Source File Directory Search

    Using #include "filename" to find local files.

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    Conditional Compilation

    Compile specific code sections based on conditions.

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    #ifdef Directive

    Checks if a macro is defined, executes corresponding code.

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    #ifdef

    A preprocessor directive that checks if a macro is defined.

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    #else

    A preprocessor directive that provides an alternative to #ifdef.

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    #endif

    A preprocessor directive that marks the end of an #ifdef block.

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    macro_name

    The name of the macro checked by #ifdef.

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    clrscr()

    A function that clears the screen in a console application.

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    printf()

    A function that outputs formatted text to the console.

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    #define

    A preprocessor directive that defines a macro.

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    #if directive

    Preprocessor directive that executes code based on a condition.

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    #else directive

    Executes alternative code if the #if condition is false.

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    #elif directive

    Allows multiple conditions in preprocessor directives.

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    #endif directive

    Marks the end of a conditional preprocessor block.

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    Preprocessor

    Software that modifies code before compilation based on directives.

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    scanf function

    Standard function to read input from the user in C.

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    printf function

    Standard function to print output to the console in C.

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    Macro Definitions

    Named constants or functions in C that are defined for use in preprocessor directives.

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    Macro

    A name defined with #define that represents a value or expression.

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    Scope

    The context in which a macro or constant is valid or accessible.

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    Compile Time Error

    An error detected by the compiler before the code runs.

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    Study Notes

    Preprocessors in C

    • Preprocessor directives are processed before compilation, typically at the start of a program.
    • They begin with a '#' symbol.
    • Preprocessors are also known as macro processors.
    • Three main types of preprocessor directives exist: macro substitution, file inclusion, and conditional compilation.

    Macro Substitution

    • Macros are named code snippets within a program.
    • The compiler replaces the name with the code whenever it encounters it.
    • The #define directive is used to define macros.
    • Example syntax: #define token value or #define first_part second_part.
    • No semicolon is needed after a macro definition.
    • An example macro definition: #define SIZE 10.

    File Inclusion

    • This directive includes external files into the source code.
    • Header files are typically included using this directive.
    • Standard syntax: #include <filename>. (compiler searches standard directories)
    • Alternate syntax with quotes: #include "filename" (compiler searches current directory and standard directories)

    Conditional Compilation

    • This allows conditional inclusion or exclusion of code parts during compilation.

    • #ifdef: Checks if a macro is defined.

    • If defined, the code block after #ifdef is compiled; otherwise, the code after #else (if present) is compiled.

    • #endif: Marks the end of a conditional block.

    • Example syntax:

      #ifdef macro_name
//code
#else
//alternative code
#endif

    • #if: Evaluates a conditional expression.

    • If true, the code block within #if is processed; otherwise, the code after #else (if present) or #elif(if present) is processed.

    • #elif: used for additional conditions.

    • #endif : Marks the end of all conditional blocks.

    • #undef: Removes a macro definition, useful for declaring variables with same names in different scope of the code or to limit scope of preprocessor constant, like macro.

    • Example syntax: #undef token.

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    Preprocessors in C PDF

    Description

    Test your knowledge of preprocessor directives in C with this quiz. Explore concepts like macros, the use of #define, and the significance of directives such as #include and #if. Perfect for students looking to strengthen their understanding of C programming.

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