详细解析C语言中的开方实现

  double sqrt(double x);

#include <math.h>
main(){
  double root;
  root = sqrt(200);
  printf("answer is %f\n", root);
}

 /** 
   * 创新工厂2014年校招算法题目，求整数N的开方，精度为0.001 
   */ 
   
  #include <stdio.h> 
  #include <stdlib.h> 
  #include <math.h> 
   
  #define ACCURACY 0.001 
   
  double newSqrt(double n) 
  { 
    double low, high, mid, tmp; 
   
    // 获取上下界 
    if (n > 1)  { 
      low = 1; 
      high = n; 
    } else { 
      low = n; 
      high = 1; 
    } 
   
    // 二分法求开方 
    while (low <= high) { 
      mid = (low + high) / 2.000; 
   
      tmp = mid * mid; 
   
      if (tmp - n <= ACCURACY && tmp -n >= ACCURACY * -1) { 
        return mid; 
      } else if (tmp > n) { 
        high = mid; 
      } else { 
        low = mid; 
      } 
    } 
   
    return -1.000; 
  } 
   
  int main(void) 
  { 
    double n, res; 
   
    while (scanf("%lf", &n) != EOF) { 
      res = newSqrt(n); 
      printf("%lf\n", res); 
    } 
   
    return 0; 
  }