>https://www.ngdc.noaa.gov/geomag/WMM/wmm_wdownload.shtml
>WMM2020_Windows.zip
https://www.ngdc.noaa.gov/geomag/WMM/soft.shtml#downloads
>what do I use instead of them
Include your own if your compiler doesn't know it:
#include <string.h>
#include<ctype.h>
char strlwr(char str) {
unsigned char p = (unsigned char )str;
while (*p) {
p = tolower((unsigned char)p);
p++;}
return str;}