The LaTeX command for mathbb C (ℂ) is \mathbb{C} (complex numbers).
\mathbb{C}Writing a paper? The table generator and the BibTeX cleaner are one click away, no account.
Write \mathbb{C} inside math mode, that is between $…$ for inline math or in a \[ … \] or equation block for display math. This symbol needs the amssymb package, so add \usepackage{amssymb} to your preamble.
Set notation lives in math mode: write $\mathbb{C}$, even in the middle of a sentence. With unicode-math under XeLaTeX or LuaLaTeX, typing ℂ in a formula gives the same symbol. Not to be confused with \mathbb{H} (ℍ).
$A \mathbb{C} B$Open this example in the live preview: it renders as you type, with no compiler and no signup.
\mathbb{H} (ℍ)\mathbb{O} (𝕆)\emptyset\varnothing\mathbb{N}\mathbb{Z}\mathbb{Q}\mathbb{R}\mathbb{F}^\complement\bigcap\bigcup\bigsqcup\uplus\biguplus\mathcal{P}Set symbols in LaTeX: the full table or search all 350+ LaTeX symbols.
Use \mathbb{C} in math mode after adding \usepackage{amssymb} to your preamble. For example, $A \mathbb{C} B$.
It comes from the amssymb package: add \usepackage{amssymb} to your preamble.