已知三角形三边长求面积

#include<stdio.h>
#include<math.h>
#include<conio.h>
float areatri(float a,float b,float    c);
float main()
{
    float a,b,c;
    float s;
    char d;
loop:
    printf("输入三角形三边长，以空格隔开\n");
    scanf("%f %f %f",&a,&b,&c);
    s=areatri(a,b,c);
    if(s<=0)
        printf("error~\n");
    else
        printf("area=%f\n",s);
    printf("按1开始新计算，按2退出\n");
    scanf("%c",&c);
    d=getch();
    if(d=='1')
        goto loop;
    if(d=='2')
        ;
}
float areatri(float a,float b,float    c)
{
    float s,p;
    if(a>0&&b>0&&c>0)
    {
        p=0.5*(a+b+c);
        s=sqrt(p*(p-a)*(p-b)*(p-c));
        return s;
    }
}