为什么输入正数后还会出现-1.#IND00

#include "stdio.h"
/FOUND/
#include "math.h"
void main()
{ double a, b;
float x;
scanf("%d,%d",&a,&b);
/FOUND/
x=1/2+sqrt(a+b);
/FOUND/
printf("x=%f\n",x);
}

#include "stdio.h"
///FOUND/
#include "math.h"
void main()
{ double a, b;
float x;
scanf("%lf,%lf",&a,&b); //double输入要用%lf
//FOUND/
x=1.0/2+sqrt(a+b);  //1/2的结果是0
//FOUND/
printf("x=%f\n",x);
}