Coding Grandmaster · project 16 of 46 · premium, free for now

Set, clear and toggle

Write set_bit(n, i), clear_bit(n, i), toggle_bit(n, i) and test_bit(n, i) (True or False) using shifts and bitwise operators.

Learn

To work with a single bit, make a mask with 1 << position. OR (|) with the mask turns a bit on, AND (&) with the inverted mask (~mask) turns it off, XOR (^) flips it, and AND with the mask tests it. These four moves are the whole toolbox of low-level programming.

Your task

Write set_bit(n, i), clear_bit(n, i), toggle_bit(n, i) and test_bit(n, i) (True or False) using shifts and bitwise operators.

Stretch challenge

Use these to turn the seven lights of a display on and off with one number.

← XOR magic Every subset →

Python

Press Run to see what your program prints.

Keep going in Coding Grandmaster

Seeing the bits

Print each of 5, 12 and 255 as 8 binary digits, and write count_ones(n) that counts the 1 bits using & and >>.

Start →14

One-line bit tricks

Write is_power_of_two(n) using n & (n - 1), is_odd(n) using n & 1, and print the powers of two up to 200 using a list comprehension.

Start →15

XOR magic

Swap a and b with three XOR lines (no temporary variable), and write lonely(numbers) that returns the number that appears only once by XOR-ing everything together.

Start →17

Every subset

Write subsets(items) returning a list of every subset as a list, in the order of the counter 0 to 2^n − 1, using bit tests. Print how many subsets four items have, and the subsets of two items.

Start →18

Permission flags

With READ = 4, WRITE = 2 and EXEC = 1, write grant(perms, flag), revoke(perms, flag), has(perms, flag) and describe(perms) which returns text like r-x (r, w and x, or - for a missing one).

Start →

Practise the idea

💡 Play Binary Bits

Switch bit values to make the decimal number shown on screen.

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FAQ

Set, clear and toggle: common questions

I am stuck. What can I do?

Press Hint for a nudge, read the message next to each goal, and compare your code with the lesson text. If you still need it, Show answer reveals a model solution. Try to type it yourself rather than copy it.

Does my work get saved?

Your ticks and XP are saved in this browser, and in your account if you log in. The code you type is not stored on a server.

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