简单Demo

void diamond(int r){
    
    int x,y;
    for ( y = 0; y<=2*r; y++) {
        for (x = 0; x<=2*r; x++) {
            if (y <= x+r&& y >=x-r && y >=-x+r && y<=-x+3*r) {
                printf("*");
            }
            else{
                printf(" ");
            }
        }
        printf("\n");
    }
}

void MMapDemo(){
    
    int *p = mmap(NULL, getpagesize(), PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, 0, 0);
    
    *p = 20;
    *(p+1) = 30;
    *(p+2) = 40;
    
    printf("%d\n",p[2]);
    munmap(p, 4096);
    printf("%d\n",getpagesize());
}