Simple program to compute the mean number of blanks per line
in a text file, classified on total length base:
dumb version, changing length ranges requires modification in 2 places

LineStat.h,cc   : classify lines according to length and compute mean blank 
                  number
BlankStat.h,cc  : process lines and compute mean blank number

to compile:

c++ -Wall -o meanBlank meanBlank.cc LineStat.cc BlankStat.cc

