Example 1

scanf("%d",&n);
for(i=0;i<n;i++)
for(j=0;j<n;j++)
  printf("(%d,%d)\n",i,j);

O(Program) = O(i-loop)

= O(N) * O(j-loop)

= O(N) * O(N) * O(1)

= O(N * N)

Example 2

scanf("%d",&n);
while (n > 1)
  { n = n/2; printf("%d\n",n); }

O(Program) = O(while-loop)

= (# times loop is executed) * O(1)

2**K <= N < 2**(K+1) where K is the integer part of log base 2 of N.

= log N * O(1)

= O(log N)