Finding and replacing substrings

Hi. Our C professor gave us the following problem:

Develop a program that reads in the file /home/elliott/hw/hw2_input.txt. Your program should replace the word ”lamb” with ”sheep” and write the output back out to a file hw2_input.out. Your program should use the input file name to construct the output file name. So, if the input file name were test.txt, it would write out test.out.

I wrote a code I think will work, but for some reason Putty and TeraTerm are both hating my computer tonight so I can't try it. I'll have access to the school computer's before it's due, but not for long so I really need to work out any big kinks before I go, because I won't have much time in the computer lab to do trial and error. Does my code make sense and should it likely work or am I using commands incorrectly?

Code:

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

main(){

	FILE *fp1, *fp2;
	char str[80];
	char changeword[10] = sheep;
	char *cp;
	char OutfileName[32];

	fp1 = fopen("/home/elliott/hw/hw2_input.txt", "r");

	//create output file and name it
	strcpy(OutfileName, fp1);
	cp = memchr(OutfileName, '.', strlen(OutfileName)-1);
	strcat(Outfilename, ".out", strlen(".out"));

	fp2 = fopen(OutfileName, "w");

	//go through each line and find the lambs
	while (fgets(str, 80, fp)!=NULL){
		if (strstr(str, "lamb")!=NULL) {
		
			strcpy(lamb, changeword);
		}
		
		
		fprintf("%s\n", str);
	}
	close(fp1);
	close(fp2);
}

fopen/fclose not close! Pay attention to your compiler warning!
strcpy(OutfileName, fp1); // copy file pointer to string?!

cp = memchr(OutfileName, '.', strlen(OutfileName)-1); // why not use strchr?

Better yet, go read some tutorial before trying out your assignment!