How to decrypt simple XOR encryption

I found the following XOR encryption function on the internet:

void xor_encrypt(char *key, char *string)
{
    int i, string_length = strlen(string);
    for(i=0; i<string_length; i++)
    {
        string[i]=string[i]^key[i];
        printf("%i", string[i]);
    }
}

It works perfect, but I would like to decrypt the string also.

For example:

void xor_decrypt(char *key, char *encrypted_string)
{
    //decrypt method goes here
}

So basically after I encrypt the string, I would use the same encryption key to decrypt the previously encrypted string.

I'm pretty new to programming and I would just like to know how to decrypt the previously encrypted string. Thanks, all help is appreciated.