mgrs1.cpp

// Online C++ compiler to run C++ program online
#include <iostream>
#include <array>

int main() {
    // Latitude Band IDs start from 'C' (i.e. omit 'A' & 'B')
    const uint8_t LAT_BAND_ID_TO_MGRS_LETTER_ID_OFFSET = 2;
    
    const char* const MGRS_LETTER = "ABCDEFGHJKLMNPQRSTUVWXYZ";


    const std::array<double, 20> BAND_NORTHING = {
        -8883084.95594830438,  // -80 deg (C)
        -7991508.54271004162, 
        -7100467.04938164819, 
        -6210141.32687210384, 
        -5320655.78919156827, 
        -4432069.05689851660, 
        -3544369.90953862480,
        -2657478.70944542065, 
        -1771254.01828129962, 
        -885503.759297154844, 
        0.000000000000,       
        885503.759297154145,  
        1771254.018281299155,
        2657478.709445421118, 
        3544369.909538624808, 
        4432069.056898516603, 
        5320655.789191568270, 
        6210141.326872103848, 
        7100467.049381648190,
        7991508.542710041627,  // 72 deg (X)
    };

    double northing = 2657478;
    
    auto it = std::lower_bound(BAND_NORTHING.begin(), BAND_NORTHING.end(), northing);
    auto lat_band_id = (it - BAND_NORTHING.begin()) - 1;
    // lat_band_id is 12, BAND_NORTHING[12]
    auto lat_band_id_size = static_cast<size_t>(lat_band_id);
    
    auto mgrs1 = MGRS_LETTER[static_cast<size_t>(lat_band_id) + LAT_BAND_ID_TO_MGRS_LETTER_ID_OFFSET];

    std::cout << "Hello world! " << lat_band_id << ", " << lat_band_id_size << ", " << mgrs1;
    
    return 0;
}