Replace a specific word in the middle of the text

Finally I made it, I wrote this code and works fine. It lets you to insert a text, after that it will ask you which word you need to search for, and what is the word you need to replace with, and after that do its job and save the result to new file (temp.txt). My problem is the program can replace all the specific words except that at the end of file before EOF Here is my code

#include <stdio.h>
#include <stdlib.h>
#include<string.h>
FILE *f1,*f2;

int main()
{
int i,Repetition=0,len,len_start,len_end,word_count=0,test=0;          //The length of the Word you need to search
char ch,ch1,search_word[10],replace_word[10];                          //Array for the word you need to search for
char *ptr=&(search_word[0]),*ptr1=&(search_word[1]);                  //Pointer on the first index of the search_word array
f1=fopen("pro.txt","w");
if(!f1){                                                       //Condition if the file does not opened correctly
        printf("Error opening file\n");
        exit(1);
}else{
    printf("enter your strings\n");
    }
f2=fopen("temp.txt","w");
if(!f2){
    puts("error opening file for writing");
    exit(1);
}
    do{                                                          //Loop to print the string to the file
    ch=getchar();
    fprintf(f1,"%c",ch);
   }while(ch!=EOF);
puts("\nEnter the word you need to search for : ");
scanf("%s",search_word);                                       //Insert the word you need to search
len=strlen(search_word);                                       //Calculate the length of the searched work
printf("\nyour word length is : %d",len);                      //Print the length of the word you need to search for
printf("\n");
puts("\nEnter the word you need to replace : ");
scanf("%s",replace_word);
fclose(f1);                                                   //Close file
printf("File closed....\n");



// The process of reading and editing the file
f1=fopen("pro.txt","r");
printf("\nFile Opened for reading....\n");                 //Open file for read and edit
ch = fgetc(f1);


start:
    if(test==1)
        ch=ch1;                                          //ch1: the next letter after ch read from file
        test=1;
ch1 = fgetc(f1);
fprintf(f2,"%c",ch);
while(ch != EOF){                                         //Read file from first to EOF
    if(*ptr==ch){                                        //ch:the letter read from file    ptr: is the pointer that point to the first letter in the search word
         if((ch1>=' ' && ch1<='@')){
        if(*(ptr1)=='\0'){                              //ptr1 is the pointer that point to the next letter in search word (if ptr1 read the '\0' that mean that you reached to last letter in search word
            len_end=ftell(f2);
            fseek(f2,len_end-len,SEEK_SET);
            len_start=ftell(f2);
            fprintf(f2,"%s",replace_word);
            word_count++;
            ptr=&search_word[0];
            ptr1=&search_word[1];
            goto start;
            /*len_end=ftell(f1)-1;
            fseek(f1,len_end-len,SEEK_SET);
            len_start=ftell(f1);
            fseek(f1,0,SEEK_SET);
            while(ftell(f1)!=(len_start)){
                ch=getc(f1);
                fprintf(f2,"%c",ch);
            }  if(ftell(f1)==(len_start)){
                        fputs(replace_word,f2);
            }
            fseek(f1,len_end+1,SEEK_SET);
           //printf("test4\n"); }else{
            ptr=&search_word[0];
            ptr1=&search_word[1];
            word_count++;
            goto start;*/
            //printf("test5\n");
            }
        //printf("test3\n");
        }
ptr++ ;
ptr1++ ;

   //printf("test2\n");
   }



    goto start;
}

fclose(f1);
fclose(f2);
    return 0;
}

The look-ahead, using ch1 = fgetc(f1); is causing the range check on ch1 to fail on EOF before the last character has been processed. Try including that in the range check:

 if((ch1>=' ' && ch1<='@') || (ch1 == EOF))