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# isdigit¤ò»ÈÍѤ·¤Ê¤¤ÊýË¡¤Ïʬ¤«¤ê¤Þ¤»¤ó(--;

#include <string>
#include <iostream>
#include <algorithm>
#include <cctype>

struct fnDigit{
    bool result;
    fnDigit() : result(true){}
    fnDigit& operator()(const int c){
        result = result && isdigit(c);
        return *this;
    }
};

int main()
{
    string str;
    cin >> str;

    fnDigit f;
    f = for_each(str.begin(), str.end(), f);
    if( str.size() < 10 && f.result ){
        puts("OK");
    }else{
        puts("NG");
    }
    return 0;
}

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#include <iostream>
#include <string>
#include <algorithm>

bool not_digit(char c) { return c < '0' || c > '9'; }

int main()
{
    using namespace std;
    string str;  cin >> str;

    if (find_if(str.begin(), str.end(), not_digit) == str.end())
        cout << "OK\n";
    else
        cout << "NG\n";
}

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> bool not_digit(char c) { return c < '0' || c > '9'; }

>    if (find_if(str.begin(), str.end(), not_digit) == str.end())

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struct Not_digit {
    bool operator()(char c) { return c < '0' || c > '9'; }
};

    if (find_if(str.begin(), str.end(), Not_digit()) == str.end())