Data types (uint, int, bool, address, string) in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Data types (uint, int, bool, address, string)

Start

↓

Declare variable

↓

Assign value

↓

Check type

↓

uint?

Yes→Store unsigned integer

↓

int?

Yes→Store signed integer

↓

bool?

Yes→Store true/false

↓

address?

Yes→Store blockchain address

↓

string?

Yes→Store text

↓

Use variable

↓

End

This flow shows how a variable is declared, assigned a value, checked for its data type, and then stored accordingly before being used.

Execution Sample

Blockchain / Solidity

uint age = 30;
int temperature = -10;
bool isActive = true;
address user = 0x1234567890abcdef1234567890abcdef12345678;
string name = "Alice";

This code declares variables of different blockchain data types and assigns values to them.

Execution Table

Step	Variable	Value Assigned	Type Checked	Stored As	Notes
1	age	30	uint	unsigned integer	30 is positive, fits uint
2	temperature	-10	int	signed integer	-10 is negative, fits int
3	isActive	true	bool	boolean	true or false value
4	user	0x1234567890abcdef1234567890abcdef12345678	address	blockchain address	Hexadecimal address format
5	name	"Alice"	string	text string	Text enclosed in quotes
6	-	-	-	-	All variables declared and stored correctly

💡 All variables assigned and stored according to their data types.

Variable Tracker

Variable	Start	After Assignment	Final
age	undefined	30	30
temperature	undefined	-10	-10
isActive	undefined	true	true
user	undefined	0x1234567890abcdef1234567890abcdef12345678	0x1234567890abcdef1234567890abcdef12345678
name	undefined	"Alice"	"Alice"

Key Moments - 3 Insights

Why can't we assign a negative number to a uint variable?

Because uint means unsigned integer, it only stores zero or positive numbers. See step 1 in execution_table where 30 is stored as uint, but negative numbers like -10 go to int type as in step 2.

What is special about the address type compared to string?

Address stores a blockchain address in hexadecimal format, which is different from string that stores general text. Look at step 4 and 5 in execution_table for the difference.

Can bool store values other than true or false?

No, bool only stores true or false values. Step 3 shows bool storing true, any other value would cause an error.

Visual Quiz - 3 Questions

Look at the execution_table, what type is the variable 'temperature' assigned to?

A int

B uint

C bool

D string

💡 Hint

Check step 2 in execution_table where 'temperature' is assigned -10 and stored as int.

At which step does the variable store a blockchain address?

A Step 1

B Step 3

C Step 4

D Step 5

💡 Hint

Look at step 4 in execution_table where 'user' is assigned an address value.

If we assign false to 'isActive', how would the variable_tracker change?

A "isActive" would show true after assignment

B "isActive" would show false after assignment

C "isActive" would show "false" as a string

D "isActive" would be undefined

💡 Hint

Boolean variables store true or false values, so the variable_tracker would show false after assignment.

Concept Snapshot

Data types in blockchain:
- uint: unsigned integer (0 and up)
- int: signed integer (positive and negative)
- bool: true or false
- address: blockchain address (hex format)
- string: text in quotes
Assign values matching type to avoid errors.

Full Transcript

This lesson shows how blockchain variables are declared and assigned values of different data types: uint for positive numbers, int for negative and positive numbers, bool for true or false, address for blockchain addresses, and string for text. Each step assigns a value and stores it according to its type. Beginners often confuse uint and int because uint cannot hold negative numbers. The address type is special for blockchain addresses, different from strings. Boolean variables only accept true or false. Understanding these types helps avoid errors when writing blockchain code.