C: Older systems developing language, pretty much industry standard to the point the C-style syntax is often a feature of other languages. Its biggest issues include a massive lack of syntax sugar, such as having to do structTypeFunction(structInstance) rather than structInstance.function() as standard in more modern languages, use of header files and a precompiler (originally invented to get around memory limitations and still liked by hard-core C fans, otherwise disliked by everyone else), and lack of built-in memory safety features, which is especially infamous with its null-terminated strings, often being part of many attack vectors and bugs.

Rust: Newer memory-safe language with functional programming features, most notably const by default, and while it does use curly braces for scopes (code blocks), the general syntax is a bit alien to the C-style of languages. Due to its heavy memory safety features, which also includes a borrow checker, not to mention the functional programming aspects, it's not a drop in replacement language for C to the point you pretty much have too reimplement the algorithms in functional style.