Re: [問題] "*"畫成圓(c語言)

[aht (誠實豆沙包)]

若要用比較快的方法...
建議利用Midpoint circle algorithm...
大概寫法如下....

unsigned char f[100][100];

int main(int argc, char *argv[])
{
        int i,j;
        int r = 20;
        for(i=0;i<100;i++)
        {
                for(j=0;j<100;j++)
                {
                        f[i][j]=0;
                }

        }
        circle(r,r,r);
        for(i=0;i<2*r+1;i++)
        {
                for(j=0;j<2*r+1;j++)
                {
                        if(f[i][j])
                                printf("*");
                        else
                                printf("=");
                }
                printf("\n");
        }
        system("PAUSE");
        return EXIT_SUCCESS;
}

void circle(int cx, int cy, int radius)
{
        int error = -radius;
        int x = radius;
        int y = 0;

        while (x >= y)
        {
                plot8points(cx, cy, x, y);

                error += y;
                ++y;
                error += y;

                if (error >= 0)
                {
                        --x;
                        error -= x;
                        error -= x;
                }
        }
}

void plot8points(int cx, int cy, int x, int y)
{
        plot4points(cx, cy, x, y);
        if (x != y) plot4points(cx, cy, y, x);
}

void plot4points(int cx, int cy, int x, int y)
{
        f[cx + x][ cy + y]=1;
        if (x != 0) f[cx - x][ cy + y] =1;
        if (y != 0) f[cx + x][ cy - y]=1;
        if (x != 0 && y != 0) f[cx - x][ cy - y]=1;
}

--
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→ aht:忘了放參考文獻了...
→ aht:http://en.wikipedia.org/wiki/Midpoint_circle_algorithm