c語言從文件輸入數學公式的神奇操作

#include <stdio.h>
#include <stdlib.h>
double formula(double a, double b, double c, double d) {
  // a + b * c - d
  return
    #include "formula.txt"
  ;
}
int main() {
  double a, b, c, d, result;
  a = 1.0;
  b = 2.0;
  c = 3.0;
  d = 4.0;
  result = formula(a, b, c, d);
  printf("result = %lf\n", result);
  return 0;
}