C string find&replace

string_replace.c

#include <string.h>
#include <stdlib.h>

// Replace string in string by creating a new one
char* str_replace(char* original, const char* find, const char* replacement, const char free_original){
	// Initializations
	int found_count = 0;
	const size_t find_len = strlen(find), replacement_len = strlen(replacement);
	char* result, *presult;
	const char* poriginal = original, *found;
	// Count founds
	while(found = strstr(poriginal, find)){
		found_count++;
		poriginal = found + find_len;
	}
	// Allocate memory for output
	if(result = malloc(strlen(original) + found_count * (replacement_len - find_len) + 1)){
		// Build output string
		presult = result, poriginal = original;
		while(found = strstr(poriginal, find)){
			found_count = found - poriginal;
			memcpy(presult, poriginal, found_count);
			memcpy(presult+found_count, replacement, replacement_len);
			presult += found_count + replacement_len;
			poriginal = found + find_len;
        	}
		strcpy(presult, poriginal);
	}
	// Free old string
	if(free_original)
		free(original);
	// Return output
	return result;
}

#include <stdio.h>

// Program entry
int main(){
	// Test text replacement
	char* output = str_replace("This is a test and he is needed!", " is ", " was ", 0);
	puts(output);
	free(output);
	// Program ends successful
	return 0;
}