Your code had some mistakes, here's the fixed code
%create the file and write values to it
fid1=fopen('hw9.txt','w');
for x=[45 66 78 23 41 55 88 66 99 24 74 88]
fprintf(fid1,'%g\n',x);
end
%the for loop writes every value to the file, last one is 88, x=88
fclose(fid1);
%read the values inside the file
fid1=fopen('hw9.txt','r');
[numbers count] = fscanf(fid1,'%d');
[value index]=max(numbers); %replaced x by numbers, x value is 88
[value2 index2]=min(numbers); %same as above
fclose(fid1);
disp(numbers)
fprintf('The number of lines of intergers is %g.\n',count)
%in the next line you had count instead of index (strange mistake)
fprintf('The max number is %g in line %g.\n',value,index)
fprintf('The min number is %g in line %g.\n',value2,index2)
The max function finds the maximum value of the vector, the min finds the minimum value of the vector.
One extra feature that you might want is
fprintf('Unique Values and the times they appear\n')
disp([unique(numbers), histc(numbers,unique(numbers))])
