So I've been trying to write a really basic function to determine the difference (in days) between two dates. I am very new to C++ so as you can imagine I am very happy with my work. This function is part of a much larger code so I have missed off my includes, but the function does compile without warnings.

Just looking for some constructive criticism that a reasonable beginner can take on board.

I should add, this function takes two dates as strings in british format DD/MM/YYYY

int dateDiffs(std::string date1, std::string date2){

    int startYear, endYear;
    int startMonth, endMonth;
    int startDay, endDay;
    
    int startInDays, endInDays;

    std::map<int,int> daysInMonth;
    
    daysInMonth[1]=31;
    daysInMonth[2]=28;
    daysInMonth[3]=31;
    daysInMonth[4]=30;
    daysInMonth[5]=31;
    daysInMonth[6]=30;
    daysInMonth[7]=31;
    daysInMonth[8]=31;
    daysInMonth[9]=30;
    daysInMonth[10]=31;
    daysInMonth[11]=30;
    daysInMonth[12]=31;

    startYear = atoi(date1.substr(6,4).c_str());
    startMonth = atoi(date1.substr(3,2).c_str());
    startDay = atoi(date1.substr(0,2).c_str());

    endYear = atoi(date2.substr(6,4).c_str());
    endMonth = atoi(date2.substr(3,2).c_str());
    endDay = atoi(date2.substr(0,2).c_str());
    
    startInDays = (startYear * 365) + (startMonth * daysInMonth[startMonth]) + startDay;
    endInDays = (endYear * 365) + (endMonth * daysInMonth[endMonth]) + endDay;

    return (endInDays - startInDays);
}

I've been trying to write a really basic function to determine the difference (in days) between two dates. I am very new to C++ so as you can imagine I am very happy with my work. This function is part of a much larger code so I have missed off my includes, but the function does compile without warnings.

Just looking for some constructive criticism that a reasonable beginner can take on board.

I should add, this function takes two dates as strings in British format DD/MM/YYYY.

int dateDiffs(std::string date1, std::string date2){

    int startYear, endYear;
    int startMonth, endMonth;
    int startDay, endDay;
    
    int startInDays, endInDays;

    std::map<int,int> daysInMonth;
    
    daysInMonth[1]=31;
    daysInMonth[2]=28;
    daysInMonth[3]=31;
    daysInMonth[4]=30;
    daysInMonth[5]=31;
    daysInMonth[6]=30;
    daysInMonth[7]=31;
    daysInMonth[8]=31;
    daysInMonth[9]=30;
    daysInMonth[10]=31;
    daysInMonth[11]=30;
    daysInMonth[12]=31;

    startYear = atoi(date1.substr(6,4).c_str());
    startMonth = atoi(date1.substr(3,2).c_str());
    startDay = atoi(date1.substr(0,2).c_str());

    endYear = atoi(date2.substr(6,4).c_str());
    endMonth = atoi(date2.substr(3,2).c_str());
    endDay = atoi(date2.substr(0,2).c_str());
    
    startInDays = (startYear * 365) + (startMonth * daysInMonth[startMonth]) + startDay;
    endInDays = (endYear * 365) + (endMonth * daysInMonth[endMonth]) + endDay;

    return (endInDays - startInDays);
}

So I've been trying to write a really basic function to determine the difference (in days) between two dates. I am very new to c++ so as you can imagine I am very happy with my work. This function is part of a much larger code so I have missed off my includes, but the function does compile without warnings.

Just looking for some constructive criticism that a reasonable beginner can take on board.

EDIT: I should add, this function takes two dates as strings in british format DD/MM/YYYY

Cheers in advance!

int dateDiffs(std::string date1, std::string date2){

    int startYear, endYear;
    int startMonth, endMonth;
    int startDay, endDay;
    
    int startInDays, endInDays;

    std::map<int,int> daysInMonth;
    
    daysInMonth[1]=31;
    daysInMonth[2]=28;
    daysInMonth[3]=31;
    daysInMonth[4]=30;
    daysInMonth[5]=31;
    daysInMonth[6]=30;
    daysInMonth[7]=31;
    daysInMonth[8]=31;
    daysInMonth[9]=30;
    daysInMonth[10]=31;
    daysInMonth[11]=30;
    daysInMonth[12]=31;

    startYear = atoi(date1.substr(6,4).c_str());
    startMonth = atoi(date1.substr(3,2).c_str());
    startDay = atoi(date1.substr(0,2).c_str());

    endYear = atoi(date2.substr(6,4).c_str());
    endMonth = atoi(date2.substr(3,2).c_str());
    endDay = atoi(date2.substr(0,2).c_str());
    
    startInDays = (startYear * 365) + (startMonth * daysInMonth[startMonth]) + startDay;
    endInDays = (endYear * 365) + (endMonth * daysInMonth[endMonth]) + endDay;

    return (endInDays - startInDays);
}

So I've been trying to write a really basic function to determine the difference (in days) between two dates. I am very new to C++ so as you can imagine I am very happy with my work. This function is part of a much larger code so I have missed off my includes, but the function does compile without warnings.

Just looking for some constructive criticism that a reasonable beginner can take on board.

I should add, this function takes two dates as strings in british format DD/MM/YYYY

int dateDiffs(std::string date1, std::string date2){

    int startYear, endYear;
    int startMonth, endMonth;
    int startDay, endDay;
    
    int startInDays, endInDays;

    std::map<int,int> daysInMonth;
    
    daysInMonth[1]=31;
    daysInMonth[2]=28;
    daysInMonth[3]=31;
    daysInMonth[4]=30;
    daysInMonth[5]=31;
    daysInMonth[6]=30;
    daysInMonth[7]=31;
    daysInMonth[8]=31;
    daysInMonth[9]=30;
    daysInMonth[10]=31;
    daysInMonth[11]=30;
    daysInMonth[12]=31;

    startYear = atoi(date1.substr(6,4).c_str());
    startMonth = atoi(date1.substr(3,2).c_str());
    startDay = atoi(date1.substr(0,2).c_str());

    endYear = atoi(date2.substr(6,4).c_str());
    endMonth = atoi(date2.substr(3,2).c_str());
    endDay = atoi(date2.substr(0,2).c_str());
    
    startInDays = (startYear * 365) + (startMonth * daysInMonth[startMonth]) + startDay;
    endInDays = (endYear * 365) + (endMonth * daysInMonth[endMonth]) + endDay;

    return (endInDays - startInDays);
}