Splitting code into multiple files - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a multi-file C program

Consider a C program split into two files: main.c and helper.c. The helper.c file defines a function int add(int a, int b) that returns the sum of two integers. The main.c file calls this function and prints the result.

What will be the output when the program is compiled and run?

C

/* helper.c */
int add(int a, int b) {
    return a + b;
}

/* main.c */
#include <stdio.h>

int add(int a, int b); // function prototype

int main() {
    int result = add(3, 4);
    printf("Result: %d\n", result);
    return 0;
}

A Compilation error: undefined reference to 'add'

B Result: 34

C Runtime error: segmentation fault

D Result: 7

💡 Hint

Remember that the function add is defined in another file and declared in main.c.

The function add correctly returns the sum of 3 and 4, which is 7. The program prints this value.

❓ Predict Output

intermediate

Effect of missing header file in multi-file C program

Given two files, main.c and math_ops.c. The math_ops.c file defines a function int multiply(int x, int y). The main.c file calls multiply but does not include a header file declaring it.

What is the most likely outcome when compiling and running this program?

C

/* math_ops.c */
int multiply(int x, int y) {
    return x * y;
}

/* main.c */
#include <stdio.h>

int main() {
    int result = multiply(5, 6);
    printf("Product: %d\n", result);
    return 0;
}

A Product: 30

B Compilation error: implicit declaration of function 'multiply'

C Runtime error: segmentation fault

D Product: 0

💡 Hint

Check if the function multiply is declared before use in main.c.

Without a function prototype or header file, the compiler will warn or error about implicit declaration of multiply.

🔧 Debug

advanced

Debugging linker error in multi-file C program

You have two files: main.c and utils.c. The main.c calls a function void greet() defined in utils.c. You compile with gcc main.c only. What error will you get?

C

/* utils.c */
#include <stdio.h>

void greet() {
    printf("Hello!\n");
}

/* main.c */

void greet();

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

A Compilation error: missing prototype for greet

B Program runs and prints 'Hello!'

C Linker error: undefined reference to 'greet'

D Runtime error: segmentation fault

💡 Hint

Think about what happens if you compile only one source file but call a function defined in another.

Compiling only main.c does not link utils.c, so the linker cannot find greet.

📝 Syntax

advanced

Correct way to declare external function in multi-file C program

Which of the following is the correct way to declare a function int compute(int a, int b) defined in another file so it can be used in main.c?

A int compute(int a, int b);

B extern int compute();

C int compute();

D void compute(int a, int b);

💡 Hint

Function declarations should match the function signature exactly.

Option A declares the function with correct return type and parameter types. Option A lacks parameter types, C is old style without parameters, A has wrong return type.

🚀 Application

expert

Number of object files needed for multi-file C project

You have a C project with 4 source files: main.c, math.c, io.c, and utils.c. You compile each source file separately into object files and then link them into an executable.

How many object files will you have before linking?

A 4

B 1

C 3

D 5

💡 Hint

Each source file produces one object file when compiled separately.

Each of the 4 source files compiles into one object file, so total 4 object files before linking.