Data types (uint, int, bool, address, string) in Blockchain / Solidity

Introduction

Data types tell the computer what kind of information we want to store. They help keep data organized and safe.

When you want to store a number that can only be positive, like a token balance.

When you need to store a number that can be positive or negative, like a temperature change.

When you want to store true or false answers, like if a user is verified.

When you need to store a blockchain address to send or receive tokens.

When you want to store text, like a name or message.

Syntax

Blockchain / Solidity

uint number;  // unsigned integer (only positive)
int number;   // signed integer (positive or negative)
bool flag;    // true or false
address addr; // blockchain address
string text;  // text string

uint means the number cannot be negative.

address stores a blockchain wallet or contract location.

Examples

This stores a positive number 30 in age.

Blockchain / Solidity

uint age = 30;

This stores a number that can be negative, here -5 degrees.

Blockchain / Solidity

int temperature = -5;

This stores a true/false value, here true means active.

Blockchain / Solidity

bool isActive = true;

This stores a blockchain address in owner.

Blockchain / Solidity

address owner = 0x1234567890abcdef1234567890abcdef12345678;

This stores text, here the name "Alice".

Blockchain / Solidity

string name = "Alice";

Sample Program

This smart contract shows different data types. It stores a positive number, a negative number, a true/false value, an address, and some text. The owner is set to the person who creates the contract.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract DataTypesExample {
    uint public tokenBalance = 1000;
    int public temperature = -10;
    bool public isVerified = false;
    address public owner;
    string public greeting = "Hello, Blockchain!";

    constructor() {
        owner = msg.sender;
    }
}

Important Notes

Use uint when you know the number will never be negative.

address is special for blockchain wallets and contracts.

string stores text but can use more gas (cost) on blockchain.

Summary

uint stores positive numbers only.

int stores numbers that can be positive or negative.

bool stores true or false values.

address stores blockchain wallet or contract addresses.

string stores text messages.