Encoding and Decrypting Data with Public/Private Keys

I want to be able to encrypt data using a private key and then decrypt it using a public key of some-sorts.

The data is irrelevant as to what it is. Lets assume for sake of argument that its a string of hex and plaintext values.

Can someone illustrate a code snippet of how to encrypt using a private key and decrypt with public key in C++ ??

Thanks
NeoKid.