用C语言实现变步长复合梯形求积分，变步长辛普森法求积分，高斯法求积分。-In the C language realization become step length composite trapezoid for integral, become step length Simpson method for integral, gaussian method for integral.

使用变步长梯形法和Romberg积分法实现1到3上分别对e^x和1/x的积分-Trapezoidal method using variable step size and Romberg integration method to achieve 1-3 respectively for e ^ x and 1/x is integral