Revise paste EsEnigma

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
int main(int argc, char ** argv){
	/*
	 * Read a file. for each character, offset by N for the first value,
	 * for every other value, N+previous char value. 
	 * Example: enigma -n 3 ABC 
	 *    A+3=D=4 
	 *    B+4= G=6
	 *    C+7=J=10
	 * */
	 
	 	if(argc !=3){
		printf("Usage: %s <integer offset> <inputfile.txt>\n", argv[0]);
	return -1;
		}
 	int offset = atoi(argv[1]);
		//printf("Offset : %d\n",offset);
	FILE *file1=fopen(argv[2], "r"); //file to decode

if(file1==NULL ){
		printf("Input Files ( %s ) Not Found\n", argv[2]);
		return 0;
		}
		int count =0;
			char c;  //file io char
		unsigned	int p; // previous character Index
	while(c!=EOF){
		c =tolower(fgetc(file1));
			if (count ==0){
			p=c+offset;
			//p=offset;
			printf("char: %c  Offset: %d value: %c \n",c,offset,c+offset);
			count ++;
			offset=p;
			} 
			if (isalpha(c)>=97 || isalpha(c)<=122){
//get the previous index plus the index of the current value c 
//offset = p + (c-'a'+1);
p=p-c-'a';
printf("P: %d \n",p);
offset = p + (c-'a'+1);
		
			//p=p+ (c-'a');
		//	offset = 1;
//printf("char: %c  Offset: %d value: %c \n",c,offset, c+offset);

//deal with other non alphabet characters here
				printf(" ");
				
				}
}

//sleep(10);
//system("clear");		
	return 0;
	}