Previous Day

#include <iostream>

using namespace std;

bool isLeap(int y){
    return y%400==0 || y%4==0 && y%100!=0;
}

void previousDay(int day, int month, int year)
{
    int ms[]={31,28,31,30,31,30,31,31,30,31,30,31};
    if( isLeap(year) )
        ms[1]=29;

    if( day==1 ){
        if( month==1 ){
            cout << 31 << "/"<<12<<"/"<<year-1<<endl;
        }else{
            cout << ms[month-2] << "/"<<month-1<<"/"<<year<<endl;
        }
    }else{
        cout << day-1 << "/"<<month<<"/"<<year<<endl;
    }
}
int main()
{
   previousDay(1,3,2017);

   return 0;
}