Storage size overview in C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code snippet?

Consider the following C code that prints the size of different data types using sizeof. What will be the output?

C

#include <stdio.h>

int main() {
    printf("%zu %zu %zu\n", sizeof(char), sizeof(int), sizeof(double));
    return 0;
}

A 1 2 4

B 1 4 8

C 2 4 8

D 1 8 8

💡 Hint

Remember that char is usually 1 byte, int is commonly 4 bytes on modern systems, and double is often 8 bytes.

The sizeof operator returns the size in bytes of the given type. On most modern systems, char is 1 byte, int is 4 bytes, and double is 8 bytes.

❓ Predict Output

intermediate

What is the size of a pointer on a 64-bit system?

Given the following code, what will be the output on a typical 64-bit system?

C

#include <stdio.h>

int main() {
    int *p;
    printf("%zu\n", sizeof(p));
    return 0;
}

A 8

B 16

C 2

D 4

💡 Hint

Think about the size of pointers on 64-bit architectures.

On 64-bit systems, pointers typically occupy 8 bytes because they need to store 64-bit addresses.

❓ Predict Output

advanced

What is the output of this struct size code?

Consider this C code that prints the size of a struct with different data types. What is the output?

C

#include <stdio.h>

struct Data {
    char c;
    int i;
    double d;
};

int main() {
    printf("%zu\n", sizeof(struct Data));
    return 0;
}

A 16

B 20

C 13

D 24

💡 Hint

Remember that structs may have padding to align data properly in memory.

The struct contains a char (1 byte), followed by 3 bytes padding, an int (4 bytes), and a double (8 bytes). Due to padding for alignment, the total size is 24 bytes on typical systems.

❓ Predict Output

advanced

What is the output of this union size code?

What will this program print when it runs?

C

#include <stdio.h>

union U {
    char c;
    int i;
    double d;
};

int main() {
    printf("%zu\n", sizeof(union U));
    return 0;
}

A 16

B 4

C 8

D 1

💡 Hint

Unions allocate memory equal to the size of their largest member, possibly with padding.

The largest member is double which is 8 bytes. The union size is 8 bytes on typical systems.

🧠 Conceptual

expert

How many bytes does this bit-field struct occupy?

Given the following struct with bit-fields, how many bytes does it occupy on a typical 64-bit system?

C

struct BitField {
    unsigned int a : 3;
    unsigned int b : 5;
    unsigned int c : 6;
    unsigned int d : 18;
};

A 4

B 8

C 2

D 6

💡 Hint

Bit-fields are packed into the smallest number of bytes that can hold all bits, aligned to the base type size.

The total bits are 3 + 5 + 6 + 18 = 32 bits, which fits exactly into 4 bytes (size of unsigned int). So the struct occupies 4 bytes.