IF语句四 C++

Description
输入三角形的三条边a，b，c；如果构成三角形那么就计算三角形的面积并输出，保留2位小数，否则输出“Not a triangle.”

Sample Input
3 5 4

Sample Output
6.00

Source
ericxie

Hint
海伦公式：令d=(a+b+c)/2，面积s为d*(d-a)*(d-b)*(d-c)的平方根

#include<iostream.h>
#include<math.h>
int main()
{
cout<<"输入三边的长度"<<endl;
double a,b,c,d,s;
cin>>a>>b>>c;
d=(a+b+c)/2;

if(a+b>c||a+c>b||b+c>a)
{s=sqrt(d*(d-a)*(d-b)*(d-c));
cout<<"面积等于:"<<s<<endl;}
else
cout<<"Not a triangle";
system("PAUSE");
return 0;
}

#include<iostream.h>
#include<math.h>
double s(double x,double y,double z)
{
double d,h;
d=(x+y+z)/2;
h=sqrt(d*(d-x)*(d-y)*(d-z));
return h;
}
void main()
{
double a,b,c;
cout<<"请输入三个数："<<endl;
cin>>a>>b>>c;
if((a+b>c)||(a+c>b)||(b+c>a))
{
double h;
h=s(a,b,c);
cout<<"面积为："<<h<<endl;