#include <algorithm>
#include <cassert>
#include <cctype>
#include <string>
bool is_number(const std::string &s) {
return !s.empty() && std::all_of(s.begin(), s.end(), ::isdigit);
}
int main() {
assert(!is_number(""));
assert(is_number("123"));
assert(!is_number("123abc"));
}
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