Storage size overview in C - Step-by-Step Execution

Concept Flow - Storage size overview

Declare variable

↓

Allocate memory based on type

↓

Check size with sizeof()

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Use size for operations or info

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End

This flow shows how a variable's storage size is determined by its type and checked using sizeof() in C.

Execution Sample

C

int a;
char b;
float c;
printf("Size of a: %zu\n", sizeof(a));
printf("Size of b: %zu\n", sizeof(b));
printf("Size of c: %zu\n", sizeof(c));

This code declares variables of different types and prints their storage sizes in bytes.

Execution Table

Step	Action	Variable/Type	sizeof() Result (bytes)	Output
1	Declare variable	int a	-	-
2	Declare variable	char b	-	-
3	Declare variable	float c	-	-
4	Evaluate sizeof(a)	int a	4	Size of a: 4
5	Evaluate sizeof(b)	char b	1	Size of b: 1
6	Evaluate sizeof(c)	float c	4	Size of c: 4
7	End	-	-	-

💡 All variables declared and their sizes printed; program ends.

Variable Tracker

Variable	Start	After sizeof()
a (int)	declared	size = 4 bytes
b (char)	declared	size = 1 byte
c (float)	declared	size = 4 bytes

Key Moments - 2 Insights

Why does sizeof(char) return 1 even though char can store only a small letter?

sizeof(char) returns 1 because it measures size in bytes, and by definition, a char occupies exactly 1 byte (the smallest addressable memory unit). See execution_table rows 2 and 5.

Why do int and float both have size 4 bytes here?

On this system, both int and float types use 4 bytes of memory. This can vary by system but is common. See execution_table rows 1, 3, 4, and 6.

Visual Quiz - 3 Questions

Look at the execution_table, what is the size of variable 'b' at step 5?

A 1 byte

B 4 bytes

C 2 bytes

D 8 bytes

💡 Hint

Check the sizeof() Result column at step 5 in execution_table.

At which step does the program print the size of the float variable?

A Step 4

B Step 6

C Step 5

D Step 7

💡 Hint

Look for the output related to 'Size of c' in execution_table.

If the int type was 8 bytes instead of 4, how would the output at step 4 change?

A Size of a: 4

B Size of a: 1

C Size of a: 8

D Size of a: 2

💡 Hint

Consider how sizeof() reflects the actual memory size of the type.

Concept Snapshot

Storage size overview in C:
- Use sizeof(type_or_variable) to get size in bytes.
- char is always 1 byte.
- int and float sizes depend on system (commonly 4 bytes).
- Sizes help understand memory use and data limits.
- sizeof returns size_t, use %zu to print.
- Sizes can vary by platform.

Full Transcript

This visual execution trace shows how C determines storage sizes of variables using the sizeof operator. Variables of types int, char, and float are declared. Then sizeof is used to find their sizes in bytes. The trace shows int and float both have size 4 bytes, and char has size 1 byte on this system. The variable tracker records these sizes after sizeof is called. Key moments clarify why char is 1 byte and why int and float sizes can vary by system. The quiz tests understanding of sizes at specific steps and how changes affect output. This helps beginners see how storage size relates to variable types and memory in C.