函数名: ultoa 
 功  能: 转换一个无符号长整型数为字符串 
 用  法: #include <stdlib.h> 
         char *ultoa(unsigned long value, char *string, int radix); 
 程序例: 
#include <stdlib.h> 
 #include <stdio.h> 
int main( void ) 
 { 
    unsigned long lnumber = 3123456789L; 
    char string[25]; 
   ultoa(lnumber,string,10); 
    printf("string = %s  unsigned long = %lu\n",string,lnumber); 
   return 0; 
 }