指数求模运算

#include " iostream "
#include " stdio.h "
#include " stdlib.h "

using   namespace  std;


  int  PowerModul( int  a, int  b, int  N)
 {       int  r,r1,r0;   
        r = 1 ; r1 = a % N;
           for ( int  q = 0 ; q <= 31 ;q ++ )
          {  if ((b & 1 ) == 1 ) r = (r * r1) % N;
             r1 = (r1 * r1) % N; b >>= 1 ; 
          }
           return  r;
 }
  int  main()
 {
     int  a,b,N;
     while (scanf( " %d%d%d " , & a, & b, & N))
         printf( " %d\n " ,PowerModul(a,b,N));
      return   0 ;
 }