sorry, forgot to take out the &...
real:: testx
!now to input and figure out f(x)
write(*,*) 'Enter real number for X '
read(*,*) testx
write(*,*) 'Solving for F(X)...'
do i=1, nr_elements
read(1,*) x(i), y(i)
if(x(i) < testx < x(i+1)) then
write(*,*) 'Y = ', y(i) = (y(i+1) - y(i)) /...