Common embedded bugs and fixes in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this embedded C code snippet?

Consider the following code running on an embedded system. What will be printed?

Embedded C

#include <stdio.h>

volatile int flag = 0;

void interrupt_handler() {
    flag = 1;
}

int main() {
    while (!flag) {
        // wait for interrupt
    }
    printf("Flag set!\n");
    return 0;
}

A Flag set!

B No output (infinite loop)

C Compilation error due to volatile usage

D Runtime error due to interrupt_handler

💡 Hint

Think about the role of volatile in embedded systems.

The volatile keyword tells the compiler that flag can change unexpectedly (e.g., by an interrupt). Without volatile, the compiler might optimize the loop to an infinite loop. Here, flag is volatile, so the loop exits when flag is set by the interrupt.

❓ Predict Output

intermediate

What is the output of this pointer arithmetic code?

What will be printed by this embedded C code?

Embedded C

#include <stdio.h>

int main() {
    char buffer[5] = {1, 2, 3, 4, 5};
    char *p = buffer;
    printf("%d\n", *(p + 3));
    return 0;
}

A 3

B 5

C 4

D Compilation error due to pointer usage

💡 Hint

Remember that pointer arithmetic moves by element size.

The pointer p points to buffer[0]. Adding 3 moves it to buffer[3], which contains the value 4.

🔧 Debug

advanced

What error does this code cause?

Analyze the following embedded C code. What error will it cause when run?

Embedded C

#include <stdio.h>

int main() {
    int *ptr = NULL;
    *ptr = 10;
    printf("%d\n", *ptr);
    return 0;
}

A Undefined behavior but no crash

B Prints 10

C Compilation error due to NULL pointer assignment

D Segmentation fault (null pointer dereference)

💡 Hint

Think about what happens when you write to a null pointer.

Dereferencing a NULL pointer causes a segmentation fault (crash) because it points to an invalid memory location.

📝 Syntax

advanced

Which option causes a syntax error?

Which of the following code snippets will cause a syntax error in embedded C?

A

int x = 10
int y = 20;

B int *p = &arr[0];

C void func() { return; }

D int arr[5] = {1, 2, 3, 4, 5};

💡 Hint

Look for missing semicolons.

Option A is missing a semicolon after int x = 10, causing a syntax error.

🚀 Application

expert

How many bytes does this struct occupy?

Given the following struct on a 32-bit embedded system, how many bytes does it occupy?

Embedded C

struct Data {
    char a;
    int b;
    char c;
};

A 8 bytes

B 12 bytes

C 9 bytes

D 10 bytes

💡 Hint

Consider padding and alignment on a 32-bit system.

On a 32-bit system, int requires 4-byte alignment. The struct layout is:
- a: 1 byte
- 3 bytes padding
- b: 4 bytes
- c: 1 byte
- 3 bytes padding
Total: 12 bytes.