implicit declaration of function `initgraph'小白请教一下各位大神，这个警告该如何解决

#include<stdio.h>
#include<graphics.h>

int main()
{
    initgraph(640,480);
   
    int r=0;
    int s=5;
    while(1)
    {
        circle(320, 240, r+=5);
        if(r>200||r<10)
        {
            s=-s;
        }
        sleep(50);
    }
    return 0;
}