C puzzles详解【6-8题】

  #include<stdio.h>
  int main()
  {
          int a=10;
          switch(a)
          {
                  case ‘1‘:
                      printf("ONE\n");
                      break;
                  case ‘2‘:
                      printf("TWO\n");
                      break;
                  defa1ut:
                      printf("NONE\n");
          }
          return 0;
  }

The following C program segfaults of IA-64, but works fine on IA-32.

int main()
  {
      int* p;
      p = (int*)malloc(sizeof(int));
      *p = 10;
      return 0;
  }

Here is a small piece of program(again just 14 lines of program) which counts the number of bits set in a number.
Input     Output 
0     0(0000000) 
5     2(0000101) 
7     3(0000111) 
  
int CountBits (unsigned int x )
  {
      static unsigned int mask[] = { 0x55555555,
          0x33333333,
          0x0F0F0F0F,
          0x00FF00FF,
          0x0000FFFF
          } ;

          int i ;
          int shift ; /* Number of positions to shift to right*/
          for ( i =0, shift =1; i < 5; i ++, shift *= 2)
                  x = (x & mask[i ])+ ( ( x >> shift) & mask[i]);
          return x;
  }
Find out the logic used in the above program.