C token loop segfault issue - c

Question

So sort of new to C and I am trying to make a listener so that User has to press enter twice to completed typing there input. Then split by the new line and run all the data through a loop and send them through my functions.
I am not sure what i am doing wrong but when the loop right under "//segfaulting at loop" in the code is commented out it runs fine but when I uncomment it and have my call to "// assemble(ftemp);" commented it out it is segfaulting so i know it here just dont know what. Valgrind says the below if that helps at all.
Thanks In Advanced Pete.
==14639== Invalid read of size 1
==14639== at 0x4E7754C: ____strtod_l_internal (strtod_l.c:608)
==14639== by 0x4011F8: main (in /home)
==14639== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==14639== Process terminating with default action of signal 11 (SIGSEGV)
==14639== Access not within mapped region at address 0x0
==14639== at 0x4E7754C: ____strtod_l_internal (strtod_l.c:608)
==14639== by 0x4011F8: main (in /home)
==14639== If you believe this happened as a result of a stack
==14639== overflow in your program's main thread (unlikely but
==14639== possible), you can try to increase the size of the
==14639== main thread stack using the --main-stacksize= flag.
==14639== The main thread stack size used in this run was 8388608.
==14639== HEAP SUMMARY:
==14639== in use at exit: 0 bytes in 0 blocks
==14639== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==14639== All heap blocks were freed -- no leaks are possible
==14639== For counts of detected and suppressed errors, rerun with: -v
==14639== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
My code:
int main(int argc, char * argv[]) {
printf("Please Enter In Float (Hit Enter Twice To Exicute)\n" );
#define MAXLENGTH 1000
char Input_string[MAXLENGTH];
int ilop = 0;
for(;;++ilop)
{
Input_string[ilop] = getchar();
if (ilop > 0 && Input_string[ilop] == '\n' &&
Input_string[ilop-1] == '\n') break;
}
Input_string[ilop] = 0;
char *pch;
// printf ("Splitting string \"%s\" into tokens:\n",Input_string);
pch = strtok (Input_string,"\n");
float ftemp = atof(pch);
//printf("price:, %f\n\n",ftemp);
assemble(ftemp);
//segfaulting at loop
while (pch != NULL)
{
pch = strtok (NULL, "\n");
ftemp = atof(pch);
printf("price:, %f\n\n",ftemp);
// assemble(ftemp);
}
return 0;
}

Answer 1

To expand on what Igal S. said, you’re first setting strtok inside the loop, then using it, and not checking it until the top of the loop. So, on the last iteration, it will set pch to NULL, then pass it to atof() without checking it.
You need something like (untested):
pch = strtok (Input_string, "\n");
while (pch != NULL)
{
/* ... */
pch = strtok (NULL, "\n");
}

Answer 2

There is a possibility of array out of bound access which might lead to undefined behavior.
In the for loop at the beginning add the check
if(ilop > 999)
{
break;
}