C program hangs after creating file - c

Question

I'm doing an exercise for University, which asks:
Create a C program called 'split', which accepts a file, and a number. The program will divide the input file in two files, one called 'part1.txt' which will contain the first n bytes, and one called 'part2.txt' which will contain the other bytes.
If the input file contains less than n bytes, the file 'part2.txt' will not be created.
This is my program. What happens when I execute it, is that it creates the part1.txt file (without anything written in it) and the program hangs.
I've been looking at this for a day, but can't spot the problem. Any help?
I've compiled using:
gcc -o split split.c
When i execute it, i write:
./split text.txt 10
Where 'text.txt' is a text file containing words i accurately typed by pressing random buttons on my keyboard.
int splitter;
int fd, fd1, fd2;
char buffer[5000];
int main(int argc, char** argv){
if(argc<2){
printf("Insert 2 arguments.");
exit(1);
}
splitter = atoi(argv[2]);
if (fd=open(argv[1], O_RDONLY) < 0){
perror("Error\n");
exit(1);
} else {
if (fd1=open("part1.txt", O_RDWR | O_CREAT, S_IRWXU) <0){
perror("Error");
exit(1);
}
if(read(fd,buffer,splitter) == splitter){
write(fd1,buffer,splitter);
if (fd2=open("part2.txt", O_RDWR | O_CREAT, S_IRWXU)<0){
perror("Errore");
exit(1);
};
while (read(fd,buffer,1) ==1){
write(fd2,buffer,1);
}
close(fd1);
close(fd2);
} else {
while (read(fd,buffer,1) ==1){
write(fd1,buffer,1);
}
close(fd1);
}
close(fd);
}

Answer 1

The relational operators reside at the 6th level of C's precedence table, much higher than the assignment operators.
This statement:
if (fd=open(argv[1], O_RDONLY) < 0)
is equivalent to:
if (fd = (open(argv[1], O_RDONLY) < 0))
The < operator returns either 1 or 0, or in other words, true or false, which gets assigned to fd.
Change it to:
if ((fd = open(argv[1], O_RDONLY)) < 0)
You have the same issue in the subsequent if statement.
From Expert C Programming:
Some authorities recommend that there are only two precedence levels
to remember in C: multiplication and division come before addition and
subtraction.
Everything else should be in parentheses. We think that's
excellent advice.