Working with a program in c that reads in a file and then I have to do both 8 bit and 16 bit checksum for a program.I only have 8 bit checksum done so far.

This is what I understand

I read the file and store the information in an array of characters and at end it takes the newline feed. so for example to calculate 8 bit check sum this is what happens essentially

File has 3 letters total ( 3 a's and a newline feed)

so array holds 4 chars aaa+(newline) (97+97+97+10)

To my understanding I add all the bytes in the array then do % 256 and that is my checksum.

97 * 3 = //3 a's (small a ) pulled from ascii table from what I understand

291 + 10 = 301 // + newline

301 % 256 = cc in hex //

however I am getting confused on how to calculate the 16 bit checksum because I can't add 2 characters at a time if its a single character array? any help would be greatly appreciated