Integer overflow and underflow in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to prevent integer overflow by using a safe addition function.

Blockchain / Solidity

function safeAdd(uint8 a, uint8 b) public pure returns (uint8) {
    uint8 c = a + [1];
    require(c >= a, "Overflow detected");
    return c;
}

Drag options to blanks, or click blank then click option'

A1

Ba

Cb

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong variable name in the addition.

Adding a constant instead of the variable.

The function adds two unsigned 8-bit integers. To check overflow, it adds b to a and verifies the result is not smaller than a.

2fill in blank

medium

Complete the code to check for underflow before subtraction.

Blockchain / Solidity

function safeSub(uint8 a, uint8 b) public pure returns (uint8) {
    require(a [1] b, "Underflow detected");
    return a - b;
}

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A>=

B<

C==

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>=' causing incorrect underflow checks.

Using '==' which is too strict.

Before subtracting, the code checks that a is greater than or equal to b to avoid underflow.

3fill in blank

hard

Fix the error in the code that causes overflow when multiplying two uint8 numbers.

Blockchain / Solidity

function safeMul(uint8 a, uint8 b) public pure returns (uint8) {
    uint8 c = a * [1];
    require(b == 0 || c / b == a, "Overflow detected");
    return c;
}

Drag options to blanks, or click blank then click option'

A0

Ba

C1

Db

Attempts:

3 left

💡 Hint

Common Mistakes

Multiplying a by itself instead of b.

Using a constant instead of the variable.

The multiplication must be between a and b. The check ensures no overflow happened.

4fill in blank

hard

Fill both blanks to create a safe division function that prevents division by zero.

Blockchain / Solidity

function safeDiv(uint8 a, uint8 b) public pure returns (uint8) {
    require(b [1] 0, "Division by zero");
    return a [2] b;
}

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A!=

B/

C==

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if b equals zero instead of not equals.

Using multiplication instead of division.

The function checks that b is not zero before dividing a by b.

5fill in blank

hard

Fill all three blanks to create a safe modulo function that prevents modulo by zero.

Blockchain / Solidity

function safeMod(uint8 a, uint8 b) public pure returns (uint8) {
    require(b [1] 0, "Modulo by zero");
    uint8 c = a [2] b;
    return c [3] b;
}

Drag options to blanks, or click blank then click option'

A!=

B%

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition or subtraction instead of modulo.

Not checking for zero divisor.

The function checks that b is not zero, then calculates a % b and returns the result.