use chrono::{NaiveDate, Datelike};
fn main() {
// Define the variables as requested
let startdate = NaiveDate::from_ymd_opt(2026, 1, 15).expect("Invalid start date");
let enddate = NaiveDate::from_ymd_opt(2027, 7, 20).expect("Invalid end date");
// Call the function to get the number of completed months
let total_months = get_months_between(startdate, enddate);
println!("Start Date: {}", startdate.format("%Y-%m-%d"));
println!("End Date: {}", enddate.format("%Y-%m-%d"));
println!("Total Months: {}", total_months);
}
/// Calculates the number of completed calendar months between two NaiveDates.
fn get_months_between(start_date: NaiveDate, end_date: NaiveDate) -> i32 {
// Validate that the start date is not later than the end date
assert!(start_date <= end_date, "Start date cannot be later than the end date.");
// 1. Calculate the base month difference using years and months
let years_diff = end_date.year() - start_date.year();
let months_diff = end_date.month() as i32 - start_date.month() as i32;
let mut total_months = (years_diff * 12) + months_diff;
// 2. Adjust if the end day is earlier in the month than the start day
// (meaning the final month hasn't fully elapsed yet)
if end_date.day() < start_date.day() {
total_months -= 1;
}
total_months
}
/*
run:
Start Date: 2026-01-15
End Date: 2027-07-20
Total Months: 18
*/
