Отсечение отрезка

program otrezok;
uses crt,GraphABC;
var k,Xmin,Xmax,Ymin,Ymax,X1,X2,Y1,Y2:integer; Xn,Xk,Yn,Yk:real; a:char;
begin
clrscr;
randomize;
{write the cordinats}
writeln('if you want to write a cordinats of the line, then press ''G'' and ''Enter''.');
writeln('Else the line will have a random cordinats');
readln(a);
if a='g' then begin write('x1='); readln(x1); write('y1='); readln(y1);
write('x2='); readln(x2); write('y2='); readln(y2); end
else begin x1:=random(1000); x2:=random(1000); y1:=random(700); y2:=random(700); end;
{the size of a screen}
xmin:=250; xmax:=350; ymin:=180; ymax:=280;
 
xn:=x1; xk:=x2; yn:=y1; yk:=y2;
{graphik elements}
line(x1,y1,x2,y2);
{exchange the cordinats}
if yn<ymin then begin Xn:=x1+(x2-x1)*(ymin-y1)/(y2-y1); yn:=ymin; end;
if yk<ymin then begin Xk:=x2+(x1-x2)*(ymin-y2)/(y1-y2); yk:=ymin; end;
if yn>ymax then begin Xn:=x1+(x2-x1)*(ymax-y1)/(y2-y1); yn:=ymax; end;
if yk>ymax then begin Xk:=x2+(x1-x2)*(ymax-y2)/(y1-y2); yk:=ymax; end;
if xn<xmin then begin Yn:=y1+(y2-y1)*(xmin-x1)/(x2-x1); xn:=xmin; end;
if xk<xmin then begin Yk:=y2+(y1-y2)*(xmin-x2)/(x1-x2); xk:=xmin; end;
if xn>xmax then begin Yn:=y1+(y2-y1)*(xmax-x1)/(x2-x1); xn:=xmax; end;
if xk>xmax then begin Yk:=y2+(y1-y2)*(xmax-x2)/(x1-x2); xk:=xmax; end;
{cheaking the lokation of the line and rounding the cordinats}
if (xn>=xmin) and (xn<=xmax) then x1:=round(xn) else k:=k+2;
if (xk>=xmin) and (xk<=xmax) then x2:=round(xk) else k:=k+2;
if (yn>=ymin) and (yn<=ymax) then y1:=round(yn) else k:=k+2;
if (yk>=ymin) and (yk<=ymax) then y2:=round(yk) else k:=k+2;
{graphik elements}
rectangle(xmin,ymin,xmax,ymax);
if k<2 then line(x1,y1,x2,y2) else writeln('The line is out of the window');
readln;
end.

program otrezok;
uses crt,GraphABC;
var k,Xmin,Xmax,Ymin,Ymax,X1,X2,Y1,Y2,x3,y3,x4,y4:integer; Xn,Xk,Yn,Yk:real; a:char;
begin
clrscr;
randomize;
{write the cordinats}
writeln('if you want to write a cordinats of the line, then press ''G'' and ''Enter''.');
writeln('Else the line will have a random cordinats');
readln(a);
if a='g' then
 begin
  write('x1='); readln(x1);
  write('y1='); readln(y1);
  write('x2='); readln(x2);
  write('y2='); readln(y2);
 end
else
 begin
  x1:=random(1000);
  x2:=random(1000);
  y1:=random(700);
  y2:=random(700);
 end;
{the size of a screen}
xmin:=250; xmax:=350; ymin:=180; ymax:=280;
xn:=x1; xk:=x2; yn:=y1; yk:=y2;
{graphik elements}
clearwindow; //очистим экран и нарисуем линию
setpencolor(clRed);
line(x1,y1,x2,y2);
SetFontSize(14);
SetFontColor(clBlue);
textout(250,10,'Press Enter');
readln;
{exchange the cordinats}
if yn<ymin then begin Xn:=x1+(x2-x1)*(ymin-y1)/(y2-y1); yn:=ymin; end;
if yk<ymin then begin Xk:=x2+(x1-x2)*(ymin-y2)/(y1-y2); yk:=ymin; end;
if yn>ymax then begin Xn:=x1+(x2-x1)*(ymax-y1)/(y2-y1); yn:=ymax; end;
if yk>ymax then begin Xk:=x2+(x1-x2)*(ymax-y2)/(y1-y2); yk:=ymax; end;
if xn<xmin then begin Yn:=y1+(y2-y1)*(xmin-x1)/(x2-x1); xn:=xmin; end;
if xk<xmin then begin Yk:=y2+(y1-y2)*(xmin-x2)/(x1-x2); xk:=xmin; end;
if xn>xmax then begin Yn:=y1+(y2-y1)*(xmax-x1)/(x2-x1); xn:=xmax; end;
if xk>xmax then begin Yk:=y2+(y1-y2)*(xmax-x2)/(x1-x2); xk:=xmax; end;
{cheaking the lokation of the line and rounding the cordinats}
//координаты нужно в новые переменные
if (xn>=xmin) and (xn<=xmax) then x3:=round(xn) else k:=k+2;
if (xk>=xmin) and (xk<=xmax) then x4:=round(xk) else k:=k+2;
if (yn>=ymin) and (yn<=ymax) then y3:=round(yn) else k:=k+2;
if (yk>=ymin) and (yk<=ymax) then y4:=round(yk) else k:=k+2;
{graphik elements}
setpencolor(clGreen);//рисуем прямоугольник
rectangle(xmin,ymin,xmax,ymax);
setpencolor(clWhite);//стираем линию
line(x1,y1,x2,y2);
setpencolor(clRed); //рисуем отрезок
if k<2 then line(x3,y3,x4,y4) else writeln('The line is out of the window');
readln;
end.