Help...using strings and txt files

I have 99% of the program done and all I have left is to write the rest of the functions to replace and process the tags. What I was asked to do was to write a program to use 3 txt files. one to read in, one to contain tags to replace those in the txt file and one to print to

Code:

#include "frmlet.h"

//reads in the whole form
void read_letter(string form_txt,
	char get_form[MAX_LINE][MAX_CHAR],
	int *form_count)
{
	int i;
	freopen("form.txt","r",stdin);
	scanf("%i", form_count);

	for (i=0; i<*form_count; i++)
	{
		scanf(" %119[6\n]", get_form[i]);
	}
return;
}

//reads in the tags and replacement names
void read_tag(string tag_txt,
	char get_tag[MAX_LINE][MAX_CHAR],
	char replace[MAX_LINE][MAX_CHAR],
	int *tag_count)
{
	int i;
	char end[] = ">";

	freopen("tags.txt","r",stdin);
	scanf("%i", tag_count);

	for (i=0; i<*tag_count; i++)
	{
		scanf(" %10[^>]> %25[^\n]", get_tag[i], replace[i]);
		strcat(get_tag[i], end);
	}

return;
}

//replaces the form tags with the names
void string_replace(char get_form[MAX_LINE][MAX_CHAR],
	char get_tag[MAX_LINE][MAX_CHAR])
{
	char temp[MAX_CHAR] = "";
	char *P, *Q, *R;

	P= strstr(...,...);

	while (P!= NULL)
	{
		
		Q = P+strlen(get_tag);
		*P = '\n';

		temp[0] = '\0';
	}
return;
}
//processes the replacements
void process(char get_form[MAX_LINE][MAX_CHAR],
	int form_count,
	char get_tag[MAX_LINE][MAX_CHAR],
	char replace[MAX_LINE][MAX_CHAR],
	int tag_count)
{
	int i,j;

	for (i=0; i<form_count; i++)
		for (j=0; j<tag_count; j++)
		{
			string_replace();
		}
return;
}

//prints the new form to a text file
void print_letter(char get_form[MAX_LINE][MAX_CHAR],
	int form_count)
{
	int i;
		for (i=0; i<form_count; i++)
		{
			puts(get_form[i]);
		}
return;
}

I am stuck at the string_replace and process functions

I know I need to use strcat but where?



thx