Structs in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Solidity struct initialization?

Consider the following Solidity code snippet:

pragma solidity ^0.8.0;

contract Test {
    struct Person {
        string name;
        uint age;
    }

    Person public p = Person("Alice", 30);

    function getAge() public view returns (uint) {
        return p.age;
    }
}

What will getAge() return when called?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Test {
    struct Person {
        string name;
        uint age;
    }

    Person public p = Person("Alice", 30);

    function getAge() public view returns (uint) {
        return p.age;
    }
}

A Alice

B 30

C Compilation error

D 0

💡 Hint

Look at how the struct is initialized and what the getAge function returns.

The struct Person is initialized with name = "Alice" and age = 30. The function getAge() returns the age field, so it returns 30.

❓ Predict Output

intermediate

What is the value of the struct field after assignment?

Given this Solidity code:

pragma solidity ^0.8.0;

contract Example {
    struct Data {
        uint x;
        bool flag;
    }

    Data public d;

    function setData() public {
        d.x = 10;
        d.flag = true;
    }

    function getFlag() public view returns (bool) {
        return d.flag;
    }
}

What does getFlag() return after setData() is called?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Example {
    struct Data {
        uint x;
        bool flag;
    }

    Data public d;

    function setData() public {
        d.x = 10;
        d.flag = true;
    }

    function getFlag() public view returns (bool) {
        return d.flag;
    }
}

A 0

B false

C true

D Compilation error

💡 Hint

Check what value is assigned to d.flag in setData().

The function setData() sets d.flag to true. So, getFlag() returns true.

🔧 Debug

advanced

Why does this Solidity struct code cause a compilation error?

Examine this Solidity code snippet:

pragma solidity ^0.8.0;

contract DebugTest {
    struct Item {
        string name;
        uint price;
    }

    Item public item = Item("Book", 20);

    function updatePrice(uint newPrice) public {
        item.price = newPrice;
    }

    function getName() public view returns (string memory) {
        return item.name;
    }
}

When compiling, an error occurs related to the struct initialization line. What is the cause?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract DebugTest {
    struct Item {
        string name;
        uint price;
    }

    Item public item = Item("Book", 20);

    function updatePrice(uint newPrice) public {
        item.price = newPrice;
    }

    function getName() public view returns (string memory) {
        return item.name;
    }
}

A The code is valid and compiles without errors.

B The string literal "Book" must be declared as bytes32, not string.

C The compiler requires the constructor to initialize the struct, not inline assignment.

D Structs cannot be initialized inline with parameters in Solidity.

💡 Hint

Check Solidity version and struct initialization rules.

Since Solidity 0.8.0, structs can be initialized inline with parameters as shown. The code is valid and compiles without errors.

📝 Syntax

advanced

Which option causes a syntax error when defining a struct in Solidity?

Which of the following struct definitions will cause a syntax error in Solidity?

A struct Person { string name; uint age; }

B } ;ega tniu ;eman gnirts { nosreP tcurts

C struct Person { string name; uint age; bool isActive; }

D struct Person { string name uint age; }

💡 Hint

Look for missing punctuation in the struct fields.

Option D is missing a semicolon between string name and uint age, causing a syntax error.

🚀 Application

expert

How many items are in the array inside this struct after execution?

Consider this Solidity contract:

pragma solidity ^0.8.0;

contract Inventory {
    struct Product {
        string name;
        uint[] batchNumbers;
    }

    Product public product;

    function addBatch(uint batch) public {
        product.batchNumbers.push(batch);
    }

    function getBatchCount() public view returns (uint) {
        return product.batchNumbers.length;
    }
}

If addBatch(101) is called twice, what will getBatchCount() return?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Inventory {
    struct Product {
        string name;
        uint[] batchNumbers;
    }

    Product public product;

    function addBatch(uint batch) public {
        product.batchNumbers.push(batch);
    }

    function getBatchCount() public view returns (uint) {
        return product.batchNumbers.length;
    }
}

A 2

B 1

C 0

D Compilation error

💡 Hint

Each call to addBatch adds one element to the array.

Calling addBatch(101) twice pushes two elements into batchNumbers. So, getBatchCount() returns 2.