Static memory allocation patterns in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of static variable initialization

What is the output of this C code snippet using static variables?

Embedded C

#include <stdio.h>

void func() {
    static int count = 0;
    count++;
    printf("%d ", count);
}

int main() {
    for(int i = 0; i < 3; i++) {
        func();
    }
    return 0;
}

A 3 3 3

B 1 2 3

C 1 1 1

D 0 1 2

💡 Hint

Remember that static variables keep their value between function calls.

The static variable 'count' is initialized once to 0 and retains its value between calls. Each call increments it by 1, so the output is '1 2 3 '.

❓ Predict Output

intermediate

Static array initialization and modification

What will be the output of this code that uses a static array inside a function?

Embedded C

#include <stdio.h>

void updateArray() {
    static int arr[3] = {1, 2, 3};
    arr[0] += 1;
    arr[1] += 1;
    arr[2] += 1;
    for(int i = 0; i < 3; i++) {
        printf("%d ", arr[i]);
    }
}

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

A 2 3 4 3 4 5

B 2 3 4 2 3 4

C 1 2 3 2 3 4

D 1 2 3 1 2 3

💡 Hint

Static arrays keep their values between function calls and are modified each time.

The static array is initialized once. Each call increments each element by 1 and prints the updated array. So first call prints '2 3 4 ', second call prints '3 4 5 '.

🔧 Debug

advanced

Identify the error in static pointer usage

What error will this code produce when compiled or run?

Embedded C

#include <stdio.h>

void func() {
    static char *ptr;
    char buffer[10] = "hello";
    ptr = buffer;
    printf("%s\n", ptr);
}

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

A Undefined behavior due to pointer to local variable used after function ends

B Prints 'hello' twice without error

C Compilation error: cannot assign local array to static pointer

D Runtime error: segmentation fault on second call

💡 Hint

Think about the lifetime of local variables and static pointers.

The pointer 'ptr' is static, but it points to 'buffer', a local array that ceases to exist after func returns. Using ptr later causes undefined behavior.

📝 Syntax

advanced

Static variable declaration syntax

Which option correctly declares a static variable inside a function that retains its value between calls?

A static count int = 0;

B int static count = 0;

C static int count = 0;

D int count static = 0;

💡 Hint

The 'static' keyword comes before the type in C declarations.

The correct syntax is 'static int count = 0;'. Other options have incorrect order of keywords causing syntax errors.

🚀 Application

expert

Static memory allocation for a fixed-size buffer

You want to create a function that returns a pointer to a fixed-size buffer that retains its content between calls. Which code snippet correctly implements this using static memory allocation?

A

char* getBuffer() {
    char *buffer = malloc(20);
    return buffer;
}

B

char* getBuffer() {
    char buffer[20];
    return buffer;
}

C

char* getBuffer() {
    static char *buffer = malloc(20);
    return buffer;
}

D

char* getBuffer() {
    static char buffer[20];
    return buffer;
}

💡 Hint

Static arrays inside functions keep their memory allocated between calls without dynamic allocation.

Option D declares a static array inside the function, so the buffer persists between calls and the pointer returned is valid. Option D returns pointer to local array (invalid). Option D uses dynamic allocation but does not free memory (not static allocation). Option D mixes static pointer with malloc which is not static allocation pattern.