C语言：给定3个字符，输入n,求长度为n的所有组合

[code="c"]

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

int strpos=0;

void makeAry(char *buff,int bufflen, char *res,char *tmp,int tmplen,int pos){
int i,j;
for(i=0;i<bufflen;i++){
tmp[pos]=buff[i];
if(pos<tmplen-1){
makeAry(buff,bufflen,res,tmp,tmplen,pos+1);
}
else{
for(j=0;j<tmplen;j++){
res[strpos*tmplen+j]=tmp[j];
}
strpos++;
}
}
}

int main(int argc, char* argv[])
{
int i,j;
char buff[3];
printf("Please input three letter:",buff);
gets(buff);
char buff2[10];
printf("Please input a number:",buff2);
gets(buff2);
int len = atoi(buff2);
long reslen = 3;
for(i=0;i<len-1;i++){
reslen*=3;
}
char res = (char)malloc(reslen*len);
char tmp = (char)malloc(len);
makeAry(buff,3,res,tmp,len,0);
printf("It's %i groups:\n",reslen);
for(i=0;i<reslen;i++){
for(j=0;j<len;j++){
printf("%c",res[len*i+j]);
}
printf("\n");
}
return 0;
}
[/code]

用JAVA 写了个 不知道符不符合你的。因为手边没有C的开发环境。
[code="java"]import java.util.ArrayList;
import java.io.FileWriter;

class Test
{

public static ArrayList<String> computer(String str,String makeStr,int max,int curTimes){
    ArrayList<String> lists = new ArrayList<String>();
    String newStr = makeStr;
    for(int j=0;j<str.length();j++){
        newStr += str.charAt(j);
        int t = curTimes+1;
        if(curTimes<max){
            lists.addAll(Test.computer(str,newStr,max,t));  
        }else{
            lists.add(newStr);
        }
        newStr = makeStr;
    }
    return lists;
}


public static void main(String[] args)throws Exception
{
    String str = "abc";
    int max = 5;
    ArrayList<String> lists = Test.computer(str,"",max,0); 
    FileWriter  f3 = new FileWriter ("file3.txt");
    StringBuffer sb = new StringBuffer();
    for(int i=0;i<lists.size();i++){
        sb.append(lists.get(i)+"\r\n");
    }
    f3.write(sb.toString());
    f3.close();
}

}[/code]

问下， 这三个字符是否可以有相同的？
第二个问题：就是输入的n值是否可以比3小，这种情况怎么处理？

C31 * 5