PASCAL语言 给三角形的三个边长A,B,C，球三角形的面积

program ex212;
var a,b,c,e,s:real;
begin
write('Input a,b,c'); readln(a,b,c);
e:=(a+b+c)/2;
if e<0 then writeln('Can`t') else
begin
if e-a<=0 then writeln('Can`t') else
begin
if e-b<=0 then writeln('Can`t') else
begin
if e-c<=0 then writeln('Can`t') else
begin
s:=(a*b*sqr(c))/(sqr(a)+sqr(b))/2;
writeln('s=',s);
end;
end;
end;
end;
readln;
end.

利用海伦公式：q=（a+b+c）/2,s=√[q(q-a)(q-b)(q-c)] .
程序如下：
program xxx;
var a,b,c,s:integer; q:real;
begin
readln(a,b,c);
if (a+b>c)and(a+c>b)and(b+c>a)
and(a>0)and(b>0)and(c>0)
then
begin
q:=(a+b+c)/2;s:=sqr(q*(q-a)*(q-b)*(q-c));
end
else writeln('length of