给定一个字符串，找到最先出现的相同字符

链接：https://www.nowcoder.com/questionTerminal/2a38887ce9ec4262856b40e5ae87e557

来源：牛客网

char first_double_char(const char *str)

{

    int len=strlen(str);

    char first_double;

    bool isfound=false;

    for(int i=1;i!=len-1;i++)

    {

        char temp=str[i];

        for(int j=0;j!=i;j++)

        {

            if(str[j]==temp)

            {

                first_double=temp;

                isfound=true;    

            }

            if(isfound)

                break;

        }

        if(isfound)

                break;

    }

    return first_double;

}