分段线性插值的C++代码实现，实现了基本的插值功能和方程拟合，可供初学者使用-Piecewise linear interpolation C++ code to achieve the basic functions and interpolation equation fitted for beginners to use

用最下二乘法多项式进行曲线拟合进而插值。(With the least two multiplicative polynomial for curve fitting, and then interpolation.)