Weird Scanf Issue - c

Question

I am trying to finish a homework program that compares a string with a text file, so the user can essentially search the text file for the search term (string) in the file. I'm getting there :)
However today I'm running into a very weird issue. When it asks for the term to search for I input the text, but it never ends. I could type all day long and it still asks for input. What weird issue(s) am I overlooking? Fresh pair of eyes might help :)
/*
ask the user for a word
convert user word to LOWER CASE
open output file
open input file
test to be sure input file is open
search for target word and keep count --> how??
print results to monitor
write results to file
close files
*/
#include<stdio.h>
#include<stdlib.h>
int main (void)
{
//declare
int i =0;
int count = 0;
/*************************************************************
working with arrays and strings
*************************************************************/
char mystring[50]; //what user puts in
char target[50]; //the word in the file we are looking for
printf("input your message ");
scanf("%s", mystring);
//printf("%s", mystring);
/*************************************************************
find file, write to it, output the string, end and close file
**************************************************************/
//define text file to use
FILE *cfile;
//name of file == file
cfile = fopen("./thanksgiving_proclamation.txt", "a");
//error handling if file does not exist
if(cfile == NULL) printf("Cannot open file");
/*************************************************************
parse through file and search for string
**************************************************************/
//convert string to lowercase
for(i = 0; i < /*strlen(mystring)*/ 500; i++)//convert to string length
{
if(target[i] >= 'A' && target[i] <='Z')
//convert char between a and z into lowercase
target[i] = target[i] + 32; //makes uppercase char
}
//compare our strings
do{
//scan through file
fscanf(cfile, "%s", mystring);
//convert string to lowercase
for(i = 0; i < /*strlen(mystring)*/ 300; i++)//convert to string length
{
if(mystring[i] >= 'A' && mystring[i] <='Z')
//convert char between a and z into lowercase
mystring[i] = mystring[i] + 32; //makes uppercase char
}
if(strcmp(mystring, target) == 0)
count++;
}while(!feof(cfile));
//while(strcmp(target,"quit")!=0)//end loop
//print to file
fprintf(cfile, "%s", mystring);
//close file
fclose(cfile);
//show user file has been written
printf("\nSuccess. File has been written\n");
printf("Press Enter to Continue...");
getchar();
return 0;
}

Answer 1

You open the file in append mode:
cfile = fopen("...", "a");
and then you try to read from it.
fscanf(cfile, "%s", mystring);
For a first attempt at solving the problem, I'd try to open the file for reading, read from it inside the loop and close the file. Then open it again, this time for appending to add the mystring there (and fclose it).
Once that works, if you want to, try to see if opening in "reading and appending mode" works ...
cfile = fopen("...", "a+");

Answer 2

You don't need "&mystring", "mystring" is already the address of the array.
It would be better to use gets or getline.
You are reading the search string into mystring, but then you are also reading the file contents into mystring.

Answer 3

I think pmg has hit on the actual problem; you've opened the file in append mode, and according to my copy of H&S reading from an append stream is not permitted. You'd have to open it "a+" (append/update) in order to read and write the stream.
You should always check the result of the *scanf() call (fscanf(), sscanf(), scanf(), etc.) for success before checking feof() or ferror(), and you should never make feof() the loop test condition (since it won't return true until after you've attempted to read past the end of the file, your loop will always execute once too many times).
I'd change your loop to something like this:
for(;;)
{
if (fscanf(cfile, "%s", mystring) != 1)
{
if (feof(cfile))
{
fprintf(stderr, "Reached end of file!\n");
break; // exit loop
}
if (ferror(cfile))
{
fprintf(stderr, "Error while reading from file!\n");
break;
}
}
/**
* continue as before
*/
}

Answer 4

It ends when you hit Enter and only stores characters till a whitespace.