Ошибки: In function `main': 18 undefined reference to `WinMain' [Error] ld returned 1 exit status .Программа кодирует символ unicode в utf-8

#include <stdint.h>
#include <windows.h>
void from_unicode_to_utf8(char *out, uint32_t utf)
{
  if (utf <= 0x7F) {
    out[0] = utf;
    out[1] = 0;
  }
  else if (utf <= 0x07FF) {
    out[0] = (char) (((utf >> 6) & 0x1F) | 0xC0);
    out[1] = (char) (((utf >> 0) & 0x3F) | 0x80);
    out[2] = 0;
  }
  else if (utf <= 0xFFFF) {
    out[0] = (char) (((utf >> 12) & 0x0F) | 0xE0);
    out[1] = (char) (((utf >>  6) & 0x3F) | 0x80);
    out[2] = (char) (((utf >>  0) & 0x3F) | 0x80);
    out[3] = 0;
  }
  else if (utf <= 0x1FFFFF) {
    out[0] = (char) (((utf >> 18) & 0x07) | 0xF0);
    out[1] = (char) (((utf >> 12) & 0x3F) | 0x80);
    out[2] = (char) (((utf >>  6) & 0x3F) | 0x80);
    out[3] = (char) (((utf >>  0) & 0x3F) | 0x80);
    out[4] = 0;
  }
  else { 
    out[0] = 0xEF;  
    out[1] = 0xBF;
    out[2] = 0xBD;
    out[3] = 0;
  }
}