求 10000 以内所有高位数字小于低位数字的数,如 25,349 等该怎么编程?

#include <stdio.h> int main( void ) { for( unsigned a=0; a<=6; ++a ) for( unsigned b=a+(a!=0); b<=7; ++b ) for( unsigned c=b+(b!=0); c<=8; ++c ) for( unsigned d=c+(c!=0); d<=9; ++d ) printf( "%u\n", a*1000+b*100+c*10+d ); return 0; }