gistfile1.cpp

#include <cstdio>
#include <cstdlib>

int strlen(char *text)
{
	int i;
	for(i = 0; text[i] != '\0'; i++);
	return i;
}

char* str_replace(char *text, int b_pos, int in_len, char *out)
{
	int out_len = strlen(out);
	if(in_len == out_len)
	{
		for(int i = 0; i < in_len; i++)
			text[b_pos + i] = out[i];
		return text;
	}
	else if(in_len < out_len)
	{
		char *temp = new char[strlen(text) + (out_len - in_len)];
		for(int i = 0; i < b_pos; i++)
			temp[i] = text[i];
		for(int i = 0; i < out_len; i++)
			temp[i + b_pos] = out[i];
		for(int i = b_pos + in_len; i < strlen(text); i++)
			temp[i + (out_len - in_len)] = text[i];
		temp[strlen(text) + (out_len - in_len)] = '\0';
		return temp;
	}
	else if(in_len > out_len)
	{
		char *temp = new char[strlen(text) - (in_len - out_len)];
		for(int i = 0; i < b_pos; i++)
			temp[i] = text[i];
		for(int i = 0; i < out_len; i++)
			temp[i + b_pos] = out[i];
		for(int i = b_pos + in_len; i < strlen(text); i++)
			temp[i - (in_len - out_len)] = text[i];
		temp[strlen(text) - 1] = '\0';
		return temp;
	}
}

char up(char ch)
{
	if(ch >= 'a' && ch <= 'z')
		return ch = 'A' + (ch - 'a');
	return ch;
}

char* replace(char *text, char *in, char *out)
{
	int cur_in = 0;
	int in_len = strlen(in);
	bool found = true;
	while(found)
	{
		found = false;
		for(int i = 0; i < strlen(text); i++)
		{
			if(up(text[i]) == up(in[cur_in]))
				cur_in++;
			else
				cur_in = 0;
			if(cur_in == in_len)
			{
 				text = str_replace(text, i - in_len + 1, in_len, out);
				found = true;
				break;
			}
		}
	}
	return text;
}

int main()
{
	char *in_filename = new char[1000], *out_filename = new char[1000], *in_string = new char[1000], *out_string = new char[1000];
	
	
	printf("Input file: ");
	scanf("%s", in_filename);
	printf("In string: ");
	scanf("%s", in_string);
	printf("Out string: ");
	scanf("%s", out_string);
	printf("Output file:");
	scanf("%s", out_filename);
	

/*	in_filename = "input.txt";
	out_filename = "output.txt";
	in_string = "cat";
	out_string = "do";*/

	FILE *f = fopen(in_filename, "r+");
	char *text = new char[10000];
	fgets(text, 10000, f);
	fclose(f);

	text = replace(text, in_string, out_string);

	f = fopen(out_filename, "w+");
	fputs(text, f);
	fclose(f);

	return 0;
}