Checking if one string is a permutation of another

gistfile1.cpp

#include <iostream>
 
void build_histogram(std::string s, int * m) {
	size_t len = s.length();
	for(int i = 0; i < len; ++i)
		m[s[i]] +=1;
}
 
bool check_permutation(std::string s1, std::string s2) 
{
	int s1map[255], s2map[255];
	for(int i=0; i<255; s1map[i]=0, s2map[i]=0, ++i);
	build_histogram(s1, s1map);
	build_histogram(s2, s2map);
	for(int i=0; i<255; ++i) 
		if(s1map[i] != s2map[i]) return false;
	return true;
}
 
int main() 
{
	std::string s1, s2;
	std::cout << "Enter string 1: ";
	std::getline(std::cin, s1);
	std::cout << "Enter string 2: ";
	std::getline(std::cin, s2);
 
	std::cout << "String 1: " << s1 << std::endl;
	std::cout << "String 2: " << s2 << std::endl;
 
	bool is_permutation = check_permutation(s1, s2);
	std::cout << "String 1 " 
		<< ( is_permutation ? "IS" : "IS NOT")
		<< " a permutation of String 2." << std::endl;
 
	return 0;
}