What is efficient way to remove last line alone in a file

What is efficient way to remove last line alone in a file

I am write some data into a file line by line.
int main ()
{
char* mystring = "joe";
int i ;
FILE * pFile;
pFile = fopen ("myfile.txt", "wb");
for(i = 0 ; i < 10 ; i++){
fprintf(pFile,"%s\n",mystring);
}
fclose (pFile);
return 0;
}
I am using new line especial charater so that new data will go into next
line.
Problem is at last line i dont want newline.
Note: Just for the demo i use for loop. In real situation I used linked
list to iterate the data hence I don't the length.
Please tell me how to remove last line from file.