The Area of an Arbitrary Triangle-任意三角形的面积

//The Area of an Arbitrary Triangle-任意三角形的面积
#include<iostream>
#include<cmath>
using namespace std;

bool IsTriangle(double a,double b,double c);
void areafun(double a,double b,double c,double& area,double& s);

int main()
{
double a,b,c,s,area;
char ans;
do{
cout<<"Enter the three length of the Triangle:\n";
cin>>a>>b>>c;

if(IsTriangle(a,b,c))
areafun(a,b,c,area,s);
else
cout<<"The three length are error!\n";

cout<<"Do you want again?";
cin>>ans;
}while('Y' == ans || 'y' == ans);
return 0;

}

bool IsTriangle(double a,double b,double c)
{
if((a+b>c && a+c>b && b+c>a && abs(a-b)<c && abs(a-c)<b && abs(b-c)<a) )
return 1;
return 0;
}

void areafun(double a,double b,double c,double& area,double& s)
{
s = (a+b+c)/2;
area = sqrt(s*(s-a)*(s-b)*(s-c));
cout<<"The area of the Triangle is:"<<area<<endl;
}

Enter the three length of the Triangle:
3 4 5
The area of the Triangle is:6
Do you want again?y
Enter the three length of the Triangle:
3 4 4
The area of the Triangle is:5.56215
Do you want again?y
Enter the three length of the Triangle:
3 4 9
The three length are error!
Do you want again?y
Enter the three length of the Triangle:
4 4 4
The area of the Triangle is:6.9282
Do you want again?