The function calculates the absolute value of a specific value, i.e. it strips off the sign, so fabs(-3) is 3. To find the highest value in a row you need to loop over that row storing the current highest and replace it when you come across a higher value.

As I've already answered this in another thread here's some code (not compiled):
Code:
int arr[10];
init_arr(arr); // you have to write this; it sets up the 10 values.
int highest=arr[0]; // set highest to the first value
for (int i=1; i<10; i++)
{
  if (arr[i]>highest)
    highest = arr[i];
}
// now highest contains the highest individual value