//數字轉換為字串
char* itoa(int num,char *str,int radix)
{
    //索引表
    char index[]="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    
    //中間變數
    unsigned unum;
    
    int i=0,j,k;
    
    //確定unum的值
    //十進位制負數
    if(radix==10&&num<0)
    {
        unum=(unsigned)-num;
        str[i++]='-';
    }
    else{
        //其他情況
        unum=(unsigned)num;
    }
    
    //轉換
    do{
        str[i++]=index[unum%(unsigned)radix];
        unum/=radix;
    }while(unum);
    
    //字串結尾補上尾零
    str[i]='\0';
    
    //判斷正負
    if(str[0]=='-')
        k=1;/*十進位制負數*/
    else
        k=0;
    
    //逆序
    char temp;
    for(j=k;j<=(i-1)/2;j++)
    {
        temp=str[j];
        str[j]=str[i-1+k-j];
        str[i-1+k-j]=temp;
    }
    
    return str;
}