[acm/ two points] two points clear entry-level explanation

//r = mid
int l = 0, r = n - 1 , mid;
while(l < r) {
    
        mid = (l + r) >> 1;
        if(a[mid] >= k) r = mid;
        else l = mid + 1;
}

//l =mid
int l = 0, r = n - 1, mid;
while(l < r) {
    
          mid = (l + r + 1) >> 1;
          if(a[mid] <= k) l = mid;
          else r = mid - 1;
}