I want it to not exceed the number 31

**Hello, I tried to program a program that does after my work days so that I work two days a day in the morning and a day in the evening, but I want it to not exceed the number 31 because the month has only 31 days but when I put number 6 for example I find it written to me 32 although I used if () .

    #include <iostream>
#include <math.h>

using namespace std;

int main (){
int repos ;
cout << "entrer la date de la 2x4 : " ;
cin >> repos ;

for (int repo  ; repos <= 31 ; repos = repos + 5 ){



    cout << "\n vous travailler le : [" << repos << "] le jour / ["<< repos+1 << "] la nuit"<< endl;


};




cout << "\n          Merci d'utiliser mon application" << endl;
cout << "\n---------------> Soheyb Biaso <---------------\n" ;

}