Reading characters

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
void reads(void);

FILE * fp;
int main(void){

    fp=fopen("/Users/amywang/Dropbox/Code/guessinggame/bob.txt","r");
    if (fp==NULL){
        printf("Whoops, something went wrong.\n");
        exit(1);
    }
    reads();

    fclose(fp);
    return 0;
}

void reads(void){
    char ch;
    while ((ch=getc(fp))!=EOF){
        if (isalpha(ch)){//it's a letter
            if(isupper(ch)){//uppercase letter
                printf("%c is a letter, and its numerical position is %d.\n", ch, ch-64);
            }
            else if (islower(ch)) {//lowercase letter
                printf("%c is a letter, and its numerical position is %d.\n", ch, ch-96);
            }
        }
        else{
            printf("%d\n", -1);
        }
    }

}