#include<stdio.h>
#include<math.h>
main()
{   double a=0.0,b=0.0,c=0.0,p=0.0,area=0.0,C=0.0;
    printf("Enter a triangle on both sides and their angl\n");
    scanf("%lf%lf%lf",&a,&b,&C);
    c=sqrt(a*a+b*b-2*a*b*cos(C));
    p=0.5*(a+b+c);
    printf("C=%.2lf\n",c);
    if(p>0&&p-a>0&&p-c>0)
        {
        area=sqrt(p*(p-a)*(p-b)*(p-c));
        printf("a=%.2lf,b=%.2lf,c=%.2lf,C=%.2lf,area=%.2lf\n",a,b,c,C,area);
        }
    else
        printf("data error!");
        getch();

}

程序能运行
但是输入3
4
90
出来却是5点多...
为什么啊 谢谢
我今年才上中学