I'm trying to do an equation in C++ but it keeps outputting 1

Question

As the title says, this code is meant to calculate the probability of 2 people having the same birthday in a group of 5 but it just outputs 1, I'm fairly new to C++ so any help would be appreciated.

#include <iostream>
using namespace std;
int main(){
float p;

p=1-(364/365)*(363/365)*(362/365)*(361/365);
cout<<p;
}

Your numerator and denominator are of type integer due to which your result is also a Integer value. — Lalit kumar, Dec 21 '19 at 19:17
*I'm fairly new to C++* -- Dividing an `int` by an `int` yielding an `int` should have been covered very early, if not right away, in the C++ book or material you're using. — PaulMcKenzie, Dec 21 '19 at 19:23

score 2 · Answer 1 · answered Dec 21 '19 at 19:10

2

Put a .0 on each number, that way is treated as a double instead of an integer. Integer division (364/365) equals 0

p=1.0-(364.0/365.0)*(363.0/365.0)*(362.0/365.0)*(361.0/365.0);

answered Dec 21 '19 at 19:10

Ricardo Ortega Magaña

2,403
16
23

M Hamza Razzaq · Answer 2 · 2019-12-22T17:01:20.067

2

This is because after calculation 364/365 the calculates answer is an integer which is 0.

To make it work change it like this.

p=1-(364/365.0)*(363/365.0)*(362/365.0)*(361/365.0);

edited Dec 22 '19 at 17:01

answered Dec 21 '19 at 19:10

M Hamza Razzaq

432
2
7
15

score 1 · Answer 3 · answered Dec 21 '19 at 19:10

1

You need to cast the integers to floats as / rounds to the largest integer below the result when both types are int:

p=1-(float(364)/float(365))*(float(363)/float(365))*(float(362)/float(365))*(float(361)/float(365));

answered Dec 21 '19 at 19:10

Ash

4,611
6
27
41

I'm trying to do an equation in C++ but it keeps outputting 1

3 Answers3