Predefined macros - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the current line number using a predefined macro.

C

#include <stdio.h>

int main() {
    printf("Line number: %d\n", [1]);
    return 0;
}

Drag options to blanks, or click blank then click option'

A__DATE__

B__FILE__

C__TIME__

D__LINE__

Attempts:

3 left

💡 Hint

Common Mistakes

Using __FILE__ instead of __LINE__ which prints the file name.

Using __DATE__ or __TIME__ which print date or time, not line number.

The __LINE__ macro expands to the current line number in the source file.

2fill in blank

medium

Complete the code to print the current file name using a predefined macro.

C

#include <stdio.h>

int main() {
    printf("File name: %s\n", [1]);
    return 0;
}

Drag options to blanks, or click blank then click option'

A__FILE__

B__LINE__

C__DATE__

D__TIME__

Attempts:

3 left

💡 Hint

Common Mistakes

Using __LINE__ which gives a number, not a string.

Using __DATE__ or __TIME__ which give date or time, not file name.

The __FILE__ macro expands to the current source file name as a string.

3fill in blank

hard

Fix the error in the code to print the compilation date using a predefined macro.

C

#include <stdio.h>

int main() {
    printf("Compiled on: %s\n", [1]);
    return 0;
}

Drag options to blanks, or click blank then click option'

A__DATE__

B__LINE__

C__FILE__

D__TIME__

Attempts:

3 left

💡 Hint

Common Mistakes

Using __TIME__ which gives time, not date.

Using __FILE__ or __LINE__ which give file name or line number.

The __DATE__ macro expands to the compilation date as a string.

4fill in blank

hard

Fill both blanks to print the compilation date and time using predefined macros.

C

#include <stdio.h>

int main() {
    printf("Compiled on: %s at %s\n", [1], [2]);
    return 0;
}

Drag options to blanks, or click blank then click option'

A__DATE__

B__TIME__

C__FILE__

D__LINE__

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of date and time macros.

Using __FILE__ or __LINE__ instead of date/time macros.

__DATE__ gives the compilation date and __TIME__ gives the compilation time.

5fill in blank

hard

Fill all three blanks to print the file name, line number, and compilation time using predefined macros.

C

#include <stdio.h>

int main() {
    printf("File: %s, Line: %d, Time: %s\n", [1], [2], [3]);
    return 0;
}

Drag options to blanks, or click blank then click option'

A__FILE__

B__LINE__

C__TIME__

D__DATE__

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of macros.

Using __DATE__ instead of __TIME__ for the time.

__FILE__ gives the file name, __LINE__ the line number, and __TIME__ the compilation time.

Practice

1. Which of the following predefined macros in C gives the current line number in the source code?

easy

A. __LINE__

B. __FILE__

C. __DATE__

D. __TIME__

Solution

1. Step 1: Understand predefined macros purpose

   Predefined macros provide info about the code or environment automatically.

2. Step 2: Identify macro for line number

   __LINE__ gives the current line number in the source file.

3. Final Answer:

   __LINE__ -> Option A

4. Quick Check:

   Line number macro = __LINE__ [OK]

Hint: Line number macro always has LINE in its name [OK]

Common Mistakes:

• Confusing __FILE__ with line number
• Using __DATE__ or __TIME__ for line info
• Thinking __LINE__ is a function

2. Which of the following is the correct syntax to print the current file name using a predefined macro in C?

easy

A. printf("File: %s", FILE);

B. printf("File: %s", __FILE__);

C. printf("File: %s", _FILE_);

D. printf("File: %s", file);

Solution

1. Step 1: Recall predefined macro for file name

   The macro __FILE__ holds the current source file name as a string.

2. Step 2: Check correct syntax usage

   Using printf("File: %s", __FILE__); correctly prints the file name.

3. Final Answer:

   printf("File: %s", __FILE__); -> Option B

4. Quick Check:

   File name macro syntax = __FILE__ [OK]

Hint: Predefined macros always have double underscores before and after [OK]

Common Mistakes:

• Omitting underscores in __FILE__
• Using FILE without underscores
• Using lowercase file instead of macro

3. What will be the output of the following C code snippet?

#include <stdio.h>
int main() {
    printf("Date: %s\n", __DATE__);
    printf("Time: %s\n", __TIME__);
    return 0;
}

medium

A. Compilation error due to undefined macros

B. Date: __DATE__\nTime: __TIME__

C. Date: current date at compilation\nTime: current time at compilation

D. Date: 0000-00-00\nTime: 00:00:00

Solution

1. Step 1: Understand __DATE__ and __TIME__ macros

   These macros expand to strings representing the date and time when the code was compiled.

2. Step 2: Predict output of printf statements

   The program prints the compilation date and time as strings, not the macro names or errors.

3. Final Answer:

   Date: current date at compilation\nTime: current time at compilation -> Option C

4. Quick Check:

   __DATE__ and __TIME__ show compile date/time [OK]

Hint: __DATE__ and __TIME__ show compile time info as strings [OK]

Common Mistakes:

• Expecting runtime current date/time
• Thinking macros print their own names
• Assuming macros are undefined

4. Consider this C code snippet:

#include <stdio.h>
int main() {
    printf("Line: %d\n", LINE);
    return 0;
}

What is the problem with this code?

medium

A. LINE is not a predefined macro; it should be __LINE__

B. Missing semicolon after printf

C. printf format specifier %d is incorrect for LINE

D. No problem; code runs fine

Solution

1. Step 1: Identify the macro usage error

   The code uses LINE instead of the correct predefined macro __LINE__.

2. Step 2: Understand consequences

   Since LINE is undefined, this causes a compilation error.

3. Final Answer:

   LINE is not a predefined macro; it should be __LINE__ -> Option A

4. Quick Check:

   Predefined macros need double underscores [OK]

Hint: Predefined macros always have double underscores before and after [OK]

Common Mistakes:

• Using LINE without underscores
• Thinking %d is wrong for line number
• Ignoring missing macro error

5. You want to log the current file name, line number, and compilation date in your C program for debugging. Which code snippet correctly uses predefined macros to do this?

hard

A. printf("File: %s, Line: %d, Date: %s\n", _FILE_, _LINE_, _DATE_);

B. printf("File: %s, Line: %d, Date: %s\n", FILE, LINE, DATE);

C. printf("File: %s, Line: %d, Date: %s\n", "__FILE__", "__LINE__", "__DATE__");

D. printf("File: %s, Line: %d, Date: %s\n", __FILE__, __LINE__, __DATE__);

Solution

1. Step 1: Identify correct predefined macros

   The macros __FILE__, __LINE__, and __DATE__ provide file name, line number, and compile date respectively.

2. Step 2: Check correct usage in printf

   Using them directly without quotes and with correct underscores prints the desired info.

3. Final Answer:

   printf("File: %s, Line: %d, Date: %s\n", __FILE__, __LINE__, __DATE__); -> Option D

4. Quick Check:

   Use double underscore macros directly in printf [OK]

Hint: Use __FILE__, __LINE__, __DATE__ directly without quotes [OK]

Common Mistakes:

• Using macros without underscores
• Putting macros inside quotes (prints names, not values)
• Using single underscores instead of double