parser.c

#include <stdio.h>
#include <string.h>

void parser(char *string)
{
   int inside = 0;
   int index = 0;
   for (int i = 0; i < strlen(string); i++)
   {
      if (string[i] == '<')
      {
         inside = 1;
         continue;
      }
      else if (string[i] == '>')
      {
         inside = 0;
         continue;
      }
      if (inside == 0)
      {
         string[index] = string[i];
         index++;
      }
   }
   string[index] = '\0';
   while (string[0] == ' ')
   {
      for (int i = 0; i < strlen(string); i++)
      {
         string[i] = string[i + 1];
      }
   }

   while (string[strlen(string) - 1] == ' ')
   {
      string[strlen(string) - 1] = '\0';
   }
}

int main()
{
   char string[] = "<h1>   this is a heading   </h1>";
   parser(string);
   printf("the parser string is ~~%s~~", string);
   return 0;
}