Thread: input mail

i have function test input mail, but when i have run it, error happen thats Assertion, can you help me, fix it, i dont know fix where.thanks

Code:

//CheckerMail.h"
#include"string"
using namespace std;
class CIMail{

public :
	static bool checkpart1(char &chr);
	static bool checkpart2(string &str);
	static bool checkpart3(string &str);
	//static bool checkpart4(string &str);
	static int checkchar(string &str);

};
//CheckerMail.cpp"

#include "string"
#include <iostream>
#include "CheckerMail.h"
using namespace std;
bool CheckerMail::checpart1(string &par1){
	if(par1.length()==0)return false;
	int k=indexdot(par1);
	for(int i=k+1;i<sizeof(par1);i++)
		if(check(par1[i])){
			return true;
		}
		return false;
}

bool CheckerMail::checper2(string &par2){
	if(par2.length()==0)return false;
	int h=indexa(par2);
	int j=indexdot(par2);
	for(int i=h+1;i<j;i++)
	if(check(par2[i])||(par2[i]=='.')||(par2[i]=='_')){
		return true;
	}
	return false;
	//return true;
}
//
bool CheckerMail::checper3(string &par3){
		if(par3.length()==0)return false;
	int index=indexa(par3);
	for(int i=0;i<index;i++)
		if(check(par3[i])||(par3[i]=='%')||(par3[i]=='+')||(par3[i]=='-')||(par3[i]=='.')||(par3[i]=='_')){
		return true;
		}
	return false;
}
//
int CheckerMail::indexa(std::string &str){
	for(int i=0;i<sizeof(str);i++){
		if(str[i]=='@')return i;
	}
	return 0;

}
int CheckerMail::indexdot(std::string &str){
	int k=0;
	for(int i=0;i<sizeof(str);i++){
			if(str[i]=='.')
				return i;
	}
	//return k;
	return 0;

}
//@
bool CheckerMail::check(char &par){
	if((par>='a')&&(par<='z')||((par>='A')&&(par<='Z')))
		return true;
	return false;

}
//
bool CheckerMail::checmain(std::string &par){
	if(!checper2(par)||!checper3(par)||!checpart1(par))return false;
		return true;
	//return false;

}
///main 
#include "string"
#include <iostream>
#include "CheckerMail.h"
using namespace std;
void main(){

string str;
	cin>>str;
	cout<<CheckerMail::checmain(str);

}