A string in C is not a data type / structure such as in many modern high-level languages. Instead, it is a '\0' (NULL) terminated char array and can be declared in three ways:

char str[] = "Hello String!";
char charr[] = {'H','e','l','l','o',' ','S','t','r','i','n','g','!','\0'};
char * string = "Hello String!";

NOTE: Check the Pointers section on how to handle a char pointer as it is slightly different than the use via an array. Also note that sizeof(string) will result in 4 or 8, while sizeof(str) and sizeof(charr) will result in 14.

CAUTION: The general rule is that sizeof(arr) for an n element array of type type is n * sizeof(type). sizeof(char) however should usually be a single byte, so 1.