cppLogic errorEasy

Unsigned integer subtraction underflow error

Time: 0:00

BugFind the bug and fix the code

What it should do

Calculate positive difference or return 0 if subtrahend is larger. Example: calculateUnsignedDelta(3, 5) -> 0

What happens instead

Condition a - b < 0 is never true for unsigned types, wrapping to 4294967294

#include <iostream>

unsigned int calculateUnsignedDelta(unsigned int a, unsigned int b) {
    // Unsigned arithmetic can never be negative; a - b underflows and wraps
    if (a - b < 0) {
        return 0;
    }
    return a - b;
}

int main() {
    std::cout << calculateUnsignedDelta(3, 5) << std::endl;
    return 0;
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

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#include <iostream> unsigned int calculateUnsignedDelta(unsigned int a, unsigned int b) { // Unsigned arithmetic can never be negative; a - b underflows and wraps if (a - b < 0) { return 0; } return a - b; } int main() { std::cout << calculateUnsignedDelta(3, 5) << std::endl; return 0; }

Unsigned integer subtraction underflow error

What it should do

What happens instead

More logic errors to practise

Unsigned integer subtraction underflow error

What it should do

What happens instead

More logic errors to practise