Error in passing data into struct - c

Question

I'm getting an error on a struct call inside a function. In the code, I am converting two bytes of data into one 16-bit data and I want to store it into one of my struct variables. However, I am getting an error that I can't pinpoint. The compiler is telling me that the error is in the line unsigned int fat.sector_size = combinedBytes;. What am I doing wrong here? Thanks in advance!
EDIT: The error that I'm getting is
main.c:62:19: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘.’ token
main.c:62:19: error: expected expression before ‘.’ token`
struct fileSystem_info{
unsigned int sector_size; //Sector size
int cluster_size_in_sectors; //Cluster size in sectors
int entries_in_root_directory; //Number of entries in root directory
int sectors_per_fat; //Sectors per file allocation table
int reserved_sectors; //Number of reserved sectors on the disk
int hidden_sectors; //Number of hidden sectors on the disk
int sector_number_of_first_copy_of_fat; //Sector number of the first copy of the file allocation table
int sector_number_of_first_sector_of_root_directory; //Sector number of the first sector of the root directory
int sector_numner_of_first_sector_of_first_usable_data_cluster; //Sector number of the first sector of the first usable data cluster
};
//Converts two 8 bit data to one 16 bit data
unsigned converter(unsigned mostSignificant_bit, unsigned leastSignificant_bit){
uint16_t value = (uint16_t)(mostSignificant_bit << 8) | leastSignificant_bit;
//return((mostSignificant_bit * 256) + leastSignificant_bit);
return (value);
}
unsigned int sectorSize (){
struct fileSystem_info fat;
unsigned char first_byte = buffer[11];
printf("%hhu \n", first_byte);
unsigned char second_byte = buffer[12];
printf("%hhu \n", second_byte);
unsigned int combinedBytes = converter ((int)second_byte, (int)first_byte);
unsigned int fat.sector_size = combinedBytes;
return (combinedBytes);
}

Answer 1

Here
unsigned int fat.sector_size = combinedBytes;
remove the type
fat.sector_size = combinedBytes;
(... and perhaps have a break ... ;-)
Refering the question on version-info in the comments below:
Do something like this:
#define VERSION_MAJOR (0) /* \ */
#define VERSION_MINOR (1) /* +--<-- adjust those for upcoming releases. */
#define VERSION_MICRO (42) /* / */
struct fileSystem_info
{
unsigned int version;
unsigned int sector_size; //Sector size
...
When initialising an instance of struct fileSystem_info, do:
struct fileSystem_info fsi = {0};
fsi.version = (VERSION_MAJOR << 24) | (VERSION_MINOR << 16) | VERSION_MICRO};
Doing so allows you a maximum version number of 255.255.65535.
As you always write version to disk you could later determine which version you wrote by reading the first unsigned int version from the structure an then in decide how to go on reading. This might be relevant in case the structure and how its content is to be interpreted following version changed during the different releases of your program.

Answer 2

An identifier cannot have ..
At
unsigned int fat.sector_size = combinedBytes;
you are defining a new variable of unsigned int type, called fat.sector_size (which is an invalid identifier.
If you want to refer to the member sector_size of the fat variable, don't use the syntax for variable definition. Just write
fat.sector_size = combinedBytes;