Opening files for reading and writing

We can now create a program to open a file for reading and another file for writing. This is where our file I/O exploration will begin and will continue through the remaining chapters of this book. The following program is our starting point:

#include <stdio.h>
#include <stdlib.h>     // for exit()
#include <string.h>     // for strerror()
#include <sys/errno.h>// for errno

int main( void ) {
FILE* inputFile;
FILE* outputFile;

char inputFilename[] = "./input.data";
char outputFilename[] = "./output.data";

inputFile = fopen( inputFilename , "r" );
if( NULL == inputFile ){
fprintf( stderr, "input file: %s: %s\n", 
             inputFilename , strerror( errno ) );
exit( 1 );
}

outputFile = fopen( outputFilename , "w" );
if( NULL == outputFile ){
fprintf( stderr, "input file: %s: %s\n", 
             outputFilename , strerror( errno ) );
exit( 1 );
}

fprintf( stderr,"...