Balance checking in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Balance checking

Start

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Input: User Address

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Query Blockchain Ledger

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Find User Balance

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Return Balance

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End

The process starts by receiving a user address, then queries the blockchain ledger to find and return the user's balance.

Execution Sample

Blockchain / Solidity

def check_balance(address, ledger):
    balance = ledger.get(address, 0)
    return balance

ledger = {'0xABC123': 100, '0xDEF456': 50}
user_address = '0xABC123'
print(check_balance(user_address, ledger))

This code looks up the balance for a given user address in the ledger and returns it.

Execution Table

Step	Action	Input	Ledger State	Balance Found	Output
1	Receive user address	0xABC123	{'0xABC123': 100, '0xDEF456': 50}	N/A	N/A
2	Query ledger for address	0xABC123	{'0xABC123': 100, '0xDEF456': 50}	100	N/A
3	Return balance	0xABC123	{'0xABC123': 100, '0xDEF456': 50}	100	100
4	Print balance	N/A	N/A	N/A	100

💡 Balance found and returned for user address; execution ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
user_address	N/A	'0xABC123'	'0xABC123'	'0xABC123'	'0xABC123'
ledger	N/A	{'0xABC123': 100, '0xDEF456': 50}	{'0xABC123': 100, '0xDEF456': 50}	{'0xABC123': 100, '0xDEF456': 50}	{'0xABC123': 100, '0xDEF456': 50}
balance	N/A	N/A	100	100	100

Key Moments - 2 Insights

Why do we use ledger.get(address, 0) instead of ledger[address]?

Using ledger.get(address, 0) safely returns 0 if the address is not found, avoiding errors. This is shown in Step 2 of the execution_table where balance is found or defaults to 0.

What happens if the user address is not in the ledger?

The balance defaults to 0 because ledger.get(address, 0) returns 0 when the address is missing, preventing crashes. This is implied in Step 2 where balance would be 0 if address missing.

Visual Quiz - 3 Questions

Look at the execution_table, what is the balance found at Step 2 for address '0xABC123'?

A 100

B 50

C 0

D Undefined

💡 Hint

Check the 'Balance Found' column in Step 2 of the execution_table.

At which step is the balance returned to the caller?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look at the 'Action' column for the step where balance is returned.

If the ledger did not have the user address, what would the balance be at Step 2?

A 100

B 50

C 0

D Error

💡 Hint

Refer to the key_moments explanation about ledger.get(address, 0) default value.

Concept Snapshot

Balance checking in blockchain:
- Input user address
- Query ledger dictionary with .get(address, 0)
- Return found balance or 0 if missing
- Prevents errors if address not found
- Simple lookup returns user's token or coin balance

Full Transcript

Balance checking means finding how much money or tokens a user has on the blockchain. We start by getting the user's address. Then we look up this address in the blockchain ledger, which stores balances. If the address exists, we get the balance. If not, we return zero to avoid errors. Finally, we return this balance to the user. This process is simple and safe because it handles missing addresses gracefully.