Header and source file organization - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of program with separated header and source files

Given the following files, what is the output when the program is compiled and run?

C

// file: math_ops.h
#ifndef MATH_OPS_H
#define MATH_OPS_H

int add(int a, int b);
int multiply(int a, int b);

#endif

// file: math_ops.c
#include "math_ops.h"

int add(int a, int b) {
    return a + b;
}

int multiply(int a, int b) {
    return a * b;
}

// file: main.c
#include <stdio.h>
#include "math_ops.h"

int main() {
    int x = 3, y = 4;
    printf("Sum: %d\n", add(x, y));
    printf("Product: %d\n", multiply(x, y));
    return 0;
}

A Compilation error due to missing function definitions

B Sum: 12\nProduct: 7

C Sum: 34\nProduct: 12

D Sum: 7\nProduct: 12

💡 Hint

Remember that the header file declares functions and the source file defines them.

The header file math_ops.h declares the functions add and multiply. The source file math_ops.c defines these functions. The main.c file includes the header and calls these functions. The output is the sum and product of 3 and 4, which are 7 and 12 respectively.

❓ Predict Output

intermediate

Result of including header file multiple times

What will happen if a header file without include guards is included multiple times in a source file?

C

// file: utils.h
int square(int x) { return x * x; }

// file: main.c
#include "utils.h"
#include "utils.h"

int main() {
    int val = 5;
    return square(val);
}

A Compilation error due to multiple definitions of square

B Program runs and returns 25

C Runtime error due to duplicate function

D Warning but program compiles and runs

💡 Hint

Think about what happens when the same function is defined twice in one translation unit.

Including the header file twice without include guards causes the function square to be defined twice in the same source file, leading to a compilation error due to multiple definitions.

🔧 Debug

advanced

Identify the cause of linker error in multi-file project

You have these files. Why does the linker give an 'undefined reference' error for function greet() when compiling main.c?

C

// file: greet.h
#ifndef GREET_H
#define GREET_H

void greet(void);

#endif

// file: main.c
#include "greet.h"

int main() {
    greet();
    return 0;
}

A greet() function is declared but not defined in any source file linked

B Missing include guard in greet.h causes multiple definitions

C greet() is defined static in another source file

D main.c is missing #include <stdio.h>

💡 Hint

Check if the function greet() has a definition linked during compilation.

The header greet.h declares greet(), but no source file defines it. The linker cannot find the function implementation, causing an undefined reference error.

📝 Syntax

advanced

Correct syntax for include guards in header files

Which option shows the correct way to write include guards in a header file named config.h?

A #define CONFIG_H\n#ifndef CONFIG_H\n// declarations\n#endif

B #ifndef CONFIG_H\n// declarations\n#define CONFIG_H\n#endif

C #ifndef CONFIG_H\n#define CONFIG_H\n// declarations\n#endif

D #ifdef CONFIG_H\n#define CONFIG_H\n// declarations\n#endif

💡 Hint

Include guards start with #ifndef and then #define the same macro.

Option C correctly uses #ifndef to check if CONFIG_H is not defined, then defines it, and ends with #endif. This prevents multiple inclusion.

🧠 Conceptual

expert

Best practice for function definitions in header files

Which statement about placing function definitions in header files is correct?

A Function definitions must always be in header files to allow inlining by the compiler.

B Function definitions should be in source files; header files only have declarations to avoid multiple definition errors.

C It's best to put all function definitions in header files to simplify compilation.

D Header files should contain only macro definitions and no functions.

💡 Hint

Think about what happens if a function is defined in a header included by multiple source files.

Defining functions in header files included by multiple source files causes multiple definitions at link time. Best practice is to put only declarations in headers and definitions in source files.