test.cpp

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <string>

using namespace std;

string::size_type find_char(const string &s, char c)
{
	string::size_type i = 0;
	while(i != s.size() && s[i] != c)
		++i;
	return i ;
}

bool is_sentence(const string &s)
{
	char b = '.';
	return (find_char(s, b) == s.size() - 1);
}

int main()
{
	string a = "adadadqeqead,";
	is_sentence(a);
}