how to fix my error saying expected expression before 'else' - c

Question

This program is intended to read a .txt file to get a set of numbers, and write to another two .txt files called even and odd as follows:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
int i=0,even,odd;
int number[i];
// check to make sure that all the file names are entered
if (argc != 3) {
printf("Usage: executable in_file output_file\n");
exit(0);
}
FILE *dog = fopen(argv[1], "r");
FILE *feven= fopen(argv[2], "w");
FILE *fodd= fopen (argv[3], "w");
// check whether the file has been opened successfully
if (dog == NULL)
{ printf("File %s cannot open!\n", argv[1]);
exit(0);
}
{ if
(i%2!=1)
i++;}
fprintf(feven, "%d", even);
fscanf(dog, "%d", &number[i]);
else {
i%2==1;
i++;}
fprintf(fodd, "%d", odd);
fscanf(dog, "%d", &number[i]);
fclose(feven);
fclose(fodd);
}

Answer 1

The { appear after the if() condition. And } should come after fscanf(dog, "%d", &number[i]);
if(i%2!=1){
i++;
fprintf(feven, "%d", even);
fscanf(dog, "%d", &number[i]);
}else {
i%2==1;
i++;
}

Answer 2

first
int i=0,even,odd;
int number[i];
means the length of Array number is 0.
you should write
if (argc != 3) {
printf("Usage: executable in_file output_file\n");
exit(0);
}
FILE *dog = fopen(argv[1], "r");
FILE *feven= fopen(argv[2], "w");
FILE *fodd= fopen (argv[3], "w");
int num;
while (fscanf(dog, "%d", &num) != EOF)
{
if(num % 2 == 0)
{
fprintf(feven, "%d", num);
}else
{
fprintf(fodd, "%d", num);
}
}
fclose(feven);
fclose(fodd);
fclose(dog);

Answer 3

{ if (i % 2 != 1)
i++;
}
fprintf(feven, "%d", even);
fscanf(dog, "%d", &number[i]);
else
{
i % 2 == 1;
i++;
}
Should be:
if (i % 2 != 1)
{
i++;
fprintf(feven, "%d", even);
fscanf(dog, "%d", &number[i]);
}
else
{
i % 2 == 1; //BTW this doesn't do anything.
i++;
}
EDIT: I've taken a few liberties so this might not be exactly your intent but it should be close enough. You need to work on a lot of small things which hopefully looking at the code will help with. Remember to understand what the functions do. And walk before you run.
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
int number;
// check to make sure that all the file names are entered
if (argc != 4)
{
printf("Usage: %s <inputfile> <even_outputfile> <odd_outputfile>\n", argv[0]);
exit(1);
}
FILE *dog = fopen(argv[1], "r");
FILE *feven = fopen(argv[2], "w");
FILE *fodd = fopen(argv[3], "w");
// check whether the file has been opened successfully
if (dog == NULL)
{
printf("File %s cannot open!\n", argv[1]);
exit(1);
}
if (feven == NULL)
{
printf("File %s cannot open!\n", argv[2]);
exit(1);
}
if (fodd == NULL)
{
printf("File %s cannot open!\n", argv[3]);
exit(1);
}
while (fscanf(dog, "%d", &number) == 1)
{
if (number % 2 == 0)
fprintf(feven, "%d ", number);
else
fprintf(fodd, "%d ", number);
}
fprintf(feven, "\n");
fprintf(fodd, "\n ");
fclose(dog);
fclose(feven);
fclose(fodd);
}