C：试图从函数中打印错误

Question

我正在创建一个函数，该函数从两行输入中获取截距并将其显示为一个点。它大部分时间都有效，但是当没有交叉点（线平行）时，我（-inf，-inf）。我试图让该功能改为打印“错误”。这是我尝试过的，但它仍然返回相同的东西。

Point getIntercept (Line a, Line b) {
    Point intercept;    
    if (a.m == b.m) {
        printf("Error");
    } else {
        double x = (a.b - b.b) / (b.m - a.m); //solves for x
        double y = a.m * x + a.b; //plugs in for y
        intercept.x = x;
        intercept.y = y;
        return intercept;
    }
}

Answer 1

没有cmets或细节的简短回答：

Point getIntercept(Line a, Line b)
{
  Point interception;
  if (a.m != b.m) {
    interception.x = fabs(b.b - a.b) / fabs(b.m - a.m);
    interception.y = a.m * interception.x + a.b;
  }
  return interception;
}

您可以像这样实现错误检查：

int intersect (Line a, Line b)
{
    return a.m != b.m || a.b == b.b;
}

然后这样称呼它：

if (intersect (a, b)) {
  Point iab = getIntercept(a, b);
  printf("interception at: %f %f\n", iab.x, iab.y);
} else {
  puts ("line a, b don't intersect");
}

带有 cmets 和详细信息的更长答案：

#include <stdio.h>
#include <math.h>
 
typedef struct Point
{
  double x;
  double y;
} Point;
 
typedef struct Line
{
  double m;
  double b;
} Line;
 
Point getIntercept(Line a, Line b)
{
  Point interception;
  if (a.m != b.m) {
    interception.x = fabs(b.b - a.b) / fabs(b.m - a.m);
    interception.y = a.m * interception.x + a.b;
  }
  return interception;
}
 
int intersect (Line a, Line b)
{
    return a.m != b.m || a.b == b.b;
}
 
int main ()
{
  Line a = {0.75, 0}; // a: y = 0.75x + 0
  Line b = {-0.5, 2}; // b: y = -0.5x + 2
  Line c = {0.75, 2}; // c: y = 0.75x + 2 => paralell to a
 
  if (intersect (a, b)) {
    Point iab = getIntercept(a, b);
    printf("interception at: %f %f\n", iab.x, iab.y);
  } else {
    puts ("line a, b don't intersect");
  }
  
  if (intersect (a, c)) {
    Point iac = getIntercept(a, c);
    printf("interception at: %f %f\n", iac.x, iac.y);
  } else {
    puts ("line a, c don't intersect");
  }
}

结果（从长答案 sn-p 生成的输出）：

interception at: 1.600000 1.200000                                                                                                                                       
line a, c don't intersect 

正如其他用户已经说过的那样：在这种情况下，要么抛出错误，要么返回有用的东西。