advertencia C4018, error C4996 y error C4716 C++ [cerrado]

Hey guys when I tried to compile my code I get these errors. Help will be greatly appreciated. regards beginner programer,

error number 1:

Warning 1 warning C4018: '<' : signed/unsigned mismatch (cpp speech analyst line 23)

error number 2:

Warning 2 warning C4018: '<' : signed/unsigned mismatch (cpp speech analyst line 31)

error number 3:

Error 3 error C4996: 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. (cpp main line 13)

error number 4:

Error 4 error C4716: 'operator<<' : must return a value (cpp main line 44)

And this is my code divided into three parts

1)

Encabezamiento

       #ifndef SPEECHANALYST_H
    #define SPEECHANALYST_H

    #include<iostream>
    #include<string>

    using namespace std;

    class SpeechAnalyst{
    private:
        std::string myData;

    public:
        SpeechAnalyst();
        void clear();
        void addData(char * stuff);
        void addStringData(std::string stuff);
        int getNumberOfWords() const;
        int getNumberOfSentences() const;
        friend ostream& operator << (ostream& outs, const SpeechAnalyst & sa);
    };

    #endif

2)

cpp Speech Analyst

#include "SpeechAnalyst.h"



SpeechAnalyst::SpeechAnalyst(){
    clear();
}

void SpeechAnalyst::clear(){
    myData = "";
} // resets everything...
void SpeechAnalyst::addData(char * stuff){
    while (*stuff++ != '\0'){
        myData += *stuff;
    }
}
void SpeechAnalyst::addStringData(std::string stuff){
    myData = stuff;
}

int SpeechAnalyst::getNumberOfWords() const{
    int countSpace = 0;
    for (int i = 0; i<(this->myData).length(); i++){
        if ((this->myData).at(i) == ' ')
            countSpace++;
    }
    return countSpace + 1;
}
int SpeechAnalyst::getNumberOfSentences() const{
    int countDot = 0;
    for (int i = 0; i<(this->myData).length(); i++){
        if ((this->myData).at(i) == '.')
            countDot++;
    }
    return countDot;

}

ostream& operator << (ostream& outs, const SpeechAnalyst &sa){
    if (sa.myData.length()>0)
        outs << "Data has " << sa.getNumberOfWords() << " words and " << sa.getNumberOfSentences() << " sentences\n";
    else
        outs << "No Data to print Out\n";
}

3)

Main cpp

#include "SpeechAnalyst.h"
#include <iostream>
#include <string>
int main(){
    SpeechAnalyst sa;
    cout << sa << endl;
    std::string speech("Fourscore and seven years ago our fathers brought forth on this continent a new nation, conceived in liberty and dedicated to the proposition that all men are created equal.");
    sa.addStringData(speech);
    cout << sa << endl;

    sa.clear();
    char * data = new char[500];
    strcpy(data, "Muffin says Hello.");
    sa.addData(data);
    cout << sa << endl;
    sa.clear();
    strcpy(data, "Muffin says Hello Muffin says Hello.");
    sa.addData(data);
    cout << sa << endl;
    sa.clear();
    strcpy(data, "Muffin says Hello. Muffin says Hello. Muffin says Hello.");
    sa.addData(data);
    cout << sa << endl;

    return 0;
}