Reading file input into a char array in c - c

Question

I am in an introductory programming class in C, and I am having some problem with our final project for the semester. We have to take an input file that will have polynomial equations on separate lines, and we have to then take the derivative of each of those equations. I am trying to read the equations into a character array so that I can then process that array to take the derivative. My logic currently calls for the program to read in one line at a time so that I can then run the corresponding array through my functions and take the derivative. I am, however, struggling to figure out how to do this, as we do not know the length of equations that will be tested.
My main function looks like this currently, and the code to execute what is described above would need to go inside the do loop before function one is called. All three functions are of type void.
int main(void)
{
char input [40], output [40];
do
{
function1( &input);
function2 (&input, &output);
function3(&output);
}while(!feof(ifp))
}
Thanks for your help.

Answer 1

the following code will get you started.
It is up to you to implement the calculateDerative() function
at the end of C programming course, the following code
should be something you can do in your sleep
#include <stdio.h>
#include <stdlib.h> // exit(), EXIT_FAILURE
#define MAX_INPUT_LEN (40)
#define MAX_OUTPUT_LEN (40)
//void function1( char * pInput );
//void function2( char * pInput, char * pOutput );
//void function3( char * pOutput );
void calculateDerivative( char* pInput, char* pOutput );
int main(void)
{
FILE *ofp = NULL;
FILE *ifp = NULL;
if( NULL == (ifp = fopen( "inputFileName", "r" ) ) )
{ // then fopen failed
perror( "fopen for read failed" );
exit( EXIT_FAILURE );
}
// implied else, fopen successful
if( NULL == (ofp = fopen( "outputFileName", "w" ) ) )
{ // then fopen failed
perror( "fopen for write failed" );
fclose( ifp );
exit( EXIT_FAILURE );
}
// implied else, fopen successful
char input [MAX_INPUT_LEN], output [MAX_OUTPUT_LEN];
while( fgets( input, sizeof(input), ifp ) ) // stay in loop until NULL returned
{
//function1( input ); // already have input available
//function2 (input, output ); // process from input to output
calculateDerivative( input, output );
//function3( output) ; // write output to output file
if( 1 != fwrite( output, strlen(output), 1, ofp ) )
{ // then fwrite failed
perror( "fwrite failed" );
fclose( ifp );
fclose( ofp );
exit( EXIT_FAILURE )
}
// implied else, fwrite successful
} // end while
fclose( ifp );
fclose( ofp );
return (0);
} // end function: main