Calculate the possible match of someone's birthday with yours

Birthdays

#include <math.h>
#include <stdio.h>

typedef struct {
	double one_match;
	double none_match;
} bday_struct;

int upto = 40;

void calculate_days(bday_struct days[]);
void print_days(bday_struct days[]);

int main(int argc, char const *argv[]) {
	
	bday_struct days[upto+1];
	calculate_days(days);
	print_days(days);

	return 0;
}  

void calculate_days(bday_struct days[]) {
   int ct;
   days[1].none_match = 1;

   for(ct=2; ct<=upto; ct ++) {
   	 days[ct].one_match = 1 - pow(364/365., ct - 1);
   	 days[ct].none_match = days[ct-1].none_match * (1 - (ct - 1)/365.);
   }
} 

void print_days(bday_struct days[]) {
   int ct;

   printf("People\tMatches me\t Any match\n");
   for(ct = 2; ct<=upto; ct ++) {
   	  printf("%i\t%.3f\t\t%.3f\n", ct, days[ct].one_match, 1 - days[ct].none_match);
   }

}