>>986
簡単なのにプログラム書かなきゃダメなの？
#include <stdio.h>
int linearly_independent( double x1, double y1,
double x2, double y2,
double x3, double y3,
double x4, double y4 ) {
return (y1-y2)*(x3-x4) == (y3-y4)*(x1-x2) ? 0 : 1;
}

int main( void ) {
double x1, y1;
double x2, y2;
double x3, y3;
double x4, y4;

printf( "変数を代入してね(はぁと):" );
scanf( "%lf %lf %lf %lf %lf %lf %lf %lf",
&x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4 );

switch (linearly_independent( x1, y1, x2, y2, x3, y3, x4, y4 )) {
case 1:
puts( "共通点を持つ" );
break;
case 0:
puts( "共通点を持たない" );
break;
}

return 0;
}