#include<graphics.h>
#include<math.h>
#define PI 3.14159
main()
{
int gd=0,gm=VGAHI,bkcolor=BLACK,color=YELLOW;
double al,l,a;
int x,y,py;
initgraph(&gd,&gm,"c:\\tc");
setbkcolor(bkcolor);
setcolor(color);

line(0,35,639,35);

for(a=0;a<=6*PI;a+=PI/100)
{
x=639/(6*PI)*a;
y=35-30*sin(a);
if(a==0)moveto(x,y);
else {lineto(x,y);}
}

if(!getch())getch();
closegraph();
}

我运行了一下,可以得到结果
能看到3个波长的正弦波.