Most languages provide built-in functions for base conversion. In Python: int(s, base) parses string s in the given base. bin(n), oct(n), hex(n) convert integer n to binary, octal, or hex strings.
In JavaScript: parseInt(s, base) parses string s. n.toString(base) converts number n to a string in the given base. C++: std::stoi(s, nullptr, base) parses s. Use std::bitset for binary.
Knowing the manual algorithms helps you understand what these functions do and lets you implement custom bases or handle edge cases. Interview problems often forbid built-ins to test your understanding.