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  1. #include <stdio.h>
  2.  
  3. //Reference: https://m...content-available-to-author-only...m.com/Collinear.html
  4.  
  5. typedef struct Point {
  6.     float x,//abscisa
  7.           y;//ordonata
  8. } TPoint;
  9.  
  10. //method number#2
  11. /*
  12. Sarrus Rule:
  13.     x1 y1 1
  14. A = x2 y2 1
  15.     x3 y3 1
  16.     x1 y1 1
  17.     x2 y1 1
  18.     x1y2 + x2y3 + x3y1 - x3y2 - x1y3-x2y1 = x1(y2-y3) - y1(x2-x3) + (x2y3-x3y2)
  19. */
  20. int checkCollinearity(TPoint P1, TPoint P2, TPoint P3) {
  21.  
  22.     return (P1.x*(P2.y-P3.y) - P1.y*(P2.x-P3.x) + P2.x*P3.y - P2.y*P3.x);
  23. }
  24.  
  25. int main(int argc, char const *argv[]) {
  26.  
  27.   TPoint P[3];
  28.  
  29.   for(int i = 0; i < 3; ++i) {
  30.      printf("Point#%d\n",i+1);
  31.      scanf("%f %f",&P[i].x, &P[i].y);
  32.   }
  33.   if(P[0].x == P[1].x || P[0].x == P[2].x) {
  34.  
  35.      if(P[2].x == P[0].x) {
  36.         printf("Collinear Points.\n");
  37.      }  else {
  38.         printf("No Collinear Points.\n");
  39.      }
  40.      //compute the slope of the line AB
  41.      //y2-y1/x2-x1
  42.   } else {
  43.      if( (P[1].y - P[0].y)/(P[1].x - P[0].x) == (P[2].y - P[1].y)/(P[2].x - P[1].x)) {
  44.          printf("Collinear Points.\n");
  45.      } else {
  46.          printf("No Collinear Points.\n");
  47.      }
  48.   }
  49.  
  50.   if(checkCollinearity(P[0],P[1],P[2]) == 0) {
  51.          printf("Collinear Points.\n");
  52.   } else {
  53.          printf("No Collinear Points.\n");
  54.   }
  55.   return 0;
  56. }
  57.  
Success #stdin #stdout 0.01s 5436KB
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Point#1
Point#2
Point#3
Collinear Points.
Collinear Points.
https://ideone.com/S0VNKe
Check Collinearity 3 Points using 2 methods (Slope and Sarrus)
language:
C (gcc 8.3)
created:
1 year ago
visibility:
secret

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