clc
close
filen='c:/usr/abc_no_n.txt'
fh=fopen(filen,'r')
%  r to read
% w to write
% a to append
i=0
a=' '
while ischar(a)==true
a=fgets(fh)
if ischar(a)==true
    b=sscanf(a,'%f %f')
    i=i+1
    fprintf('i  a  b', i,a,b)
    x(i)=b(1)
    y(i)=b(2)
end
end

sumx=0
for i=1:1:n
    sumx=sumx+x(i)*y(i)
end

filewr='c:\usr\output.txt'
fl=fopen(filewr,'w')
fprintf (fl,'th value of the summation is %f',sumx)