求助cpp(126) : warning C4715: 'getMonthValue' : not all control paths return a val

问题在最后
//函数功能：根据输入的日期来判断输出的日期是星期几。
#include<iostream>
bool isLeapYear(int year);
int getCenturyValue(int year);
int getYearVlaue(int year);
int getMonthValue(int month, int year);
void getInput(    int m_m, int m_d, int m_y);
int main()
{
    using namespace std;
    int m_month=0,m_day=0,m_year=0,r_sum,r_r;
    getInput(m_month,m_day,m_year);
    r_sum=m_day+getMonthValue(m_month,m_year)
    +getYearVlaue(m_year)+getCenturyValue(m_year);
    r_r=r_sum%7;
    switch(r_r)
    {
        case 0:
            cout<<"Sunday"<<endl;
            break;
        case 1:
            cout<<"Monday"<<endl;
            break;
        case 2:
            cout<<"Tuesday"<<endl;
            break;
        case 3:
            cout<<"Wednesday"<<endl;
            break;
        case 4:
            cout<<"Thursday"<<endl;
            break;
        case 5:
            cout<<"Friday"<<endl;
            break;
        case 6:
            cout<<"Saturday"<<endl;
            break;
    }
    return 0;
}
//判断是否为闰年
bool isLeapYear(int year)
{
    if( (year%400==0)||( (year%4==0)&&(year%100!=0) ) )
        return true;
    else
        return false;
}
//获取年份头两位
int getCenturyValue(int year)
{
    int q2_year,num;
    q2_year=year/100;
    num=(3-(q2_year%4))*2;
    return num;
}
int getYearVlaue(int year)
{
    int r_year;
    r_year=(year%100)/4+(year%100);
    return r_year;
}
//按月份返回值
int getMonthValue(int month, int year)
{
    if(month==1)
    {
        if( isLeapYear(year) )
        {
            return 6;
        }
        else
            return 0;
    }
    if(month==2)
    {
        if( isLeapYear(year) )
        {
            return 2;
        }
        else
            return 3;
    }
    if(month==3)
    {
        return 3;
    }
    if(month==4)
    {
        return 6;
    }
    if(month==5)
    {
        return 1;
    }
    if(month==6)
    {
        return 4;
    }
    if(month==7)
    {
        return 6;
    }
    if(month==8)
    {
        return 2;
    }
    if(month==9)
    {
        return 5;
    }
    if(month==10)
    {
        return 0;
    }
    if(month==11)
    {
        return 3;
    }
    if(month==12)
    {
        return 5;
    }
}
void getInput(    int m_m, int m_d, int m_y)
{
    using namespace std;
    cout<<"Please input month(number)"<<" "<<"days(number)"
        <<","<<" "<<"years"<<endl;
    cout<<"For instance:7 4,2008"<<endl;
    cin>>m_m>>m_d>>m_y;
}

G:\应用程序\判断星期\判断.cpp(126) : warning C4715: 'getMonthValue' : not all control paths return a value

谢谢