How do you draw an influence line diagram for shear at a section?

For shear influence line at section 'c' in a simply supported beam: When unit load is between left support A and section c, shear at c equals negative of reaction at A, giving IL ordinate = -x/L (sloping line). When load is between c and right support B, shear equals reaction at B, giving IL ordinate = (L-x)/L. The IL has a discontinuity at section c with a jump of 1.0, representing the shear reversal.