Encryption algorithm with the same length of ciphertext and plaintext after string encryption

Question

C++
Encryption algorithm with the same length of ciphertext and plaintext after string encryption。

I downloaded an open source library of Crypto + + on the Internet.

But I don't know which algorithms can encrypt the plaintext string, and the length of the ciphertext is the same as that of the plaintext, or the length is about the same. Can you help me, please?