Language: C

#include <stdio.h>
#include <ctype.h>int main(void) {                                                                
    double x1, y1, x2, y2, x3, y3, x4, y4;                                      
    int n;                                                                      
                                                                                    scanf("%d", &n);                                                                while (n-- > 0) {                                                           scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4);      
        if (x2 - x1 == 0)                                                                   if (x4 - x3 == 0)                                                                   printf("YES\n");                                                
            else                                                                
                printf("NO\n");                                                 
        else if (((y2 - y1) / (x2 - x1)) == ((y4 - y3) / (x4 - x3)))            
            printf("YES\n");                                                    
        else                                                                                printf("NO\n");                                                         }                                                                           
                                                                                
    return 0;                                                                   }

Compiler output:
main.c:2:19: warning: extra tokens at end of #include directive
    2 | #include <ctype.h>int main(void) {
      |                   ^~~
main.c:3:16: warning: built-in function 'y1' declared as non-function [-Wbuiltin-declaration-mismatch]
    3 |     double x1, y1, x2, y2, x3, y3, x4, y4;
      |                ^~
main.c:5:91: error: expected declaration specifiers or '...' before string constant
    5 |                                                                                     scanf("%d", &n);                                                                while (n-- > 0) {                                                           scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4);
      |                                                                                           ^~~~
main.c:5:97: error: expected declaration specifiers or '...' before '&' token
    5 |                                                                                     scanf("%d", &n);                                                                while (n-- > 0) {                                                           scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4);
      |                                                                                                 ^
main.c:5:165: error: expected identifier or '(' before 'while'
    5 |                                                                                     scanf("%d", &n);                                                                while (n-- > 0) {                                                           scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4);
      |                                                                                                                                                                     ^~~~~
main.c:13:5: error: expected identifier or '(' before 'return'
   13 |     return 0;                                                                   }
      |     ^~~~~~
main.c:13:81: error: expected identifier or '(' before '}' token
   13 |     return 0;                                                                   }
      |                                                                                 ^