named fifo C issue - c

Question

I have this C code:
#define BUFSIZE 256
int main ( int argc, char *argv[])
{
int fdIn;
int fdOut;
if( argc != 3)
{
perror("argument error");
exit(1);
}
if( (fdIn = open(argv[1], O_RDONLY ) )<0)
{
perror("pipe input error open");
exit(1);
}
if( (fdOut = open(argv[2], O_WRONLY ) )<0)
{
perror("pipe input error open");
exit(1);
}
int c = 2;
while(c--)
{
char var1[BUFSIZE];
char var2[BUFSIZE];
char string[100];
memset(var1, 0, sizeof(var1));
memset(var2, 0, sizeof(var2));
memset(string, 0, sizeof(string));
if( readLine(fdIn, var1, sizeof(var1)) == 0)
{
printf("exit1\n");
exit(0);
}
if( readLine(fdIn, var2, sizeof(var2)) == 0)
{
printf("exit2\n");
exit(0);
}
removeNewLine(var1);
removeNewLine(var2);
printf("%s\n",var1);
printf("%s\n",var2);
int n = atoi(var1);
int m = atoi(var2);
if (n!=0 && m % n == 0 ) {
sprintf(string,"multiple\n");
}
else{
sprintf(string,"negative\n");
}
printf("%s", string);
writeLine(fdOut, string, strlen(string));
}
close(fdOut);
close(fdIn);
exit(0);
}
This program accepts 2 inputs: first is input fifo's name and second is output fifo's name.
This program does this: reads in the input fifo 2 numbers and then establishes if second number is multiple of first number and then writes on output fifo "multiple" or "negative".
This all for 2 times; my problem is when it executed the second loop where the first ReadLine returns 0 and it prints exit1.
the program should not stop on the readLine pending content in the FIFO?
functions used in the program:
int readLine( int fd, char* str, int bufferSize)
{
return readToDel(fd, '\n', str, bufferSize);
}
int readToDel( int fd, char delimiter, char* str, int bufferSize)
{
int n;
int byteLetti =0;
int index=0;
do /* Read characters until NULL or end-of-input */
{
if( (n = read (fd, str+index, 1)) < 0)
{
perror("Errore: lettura dal file descriptor fallita");
exit(1);
}
byteLetti+=n;
}
while (n > 0 && *(str+index++) != delimiter && index < bufferSize);
return byteLetti; /* Return false if end-of-input */
}
For testing this program I do like this:
open first terminal and I write in the input fifo in this way:
echo "4" > input
echo "8" > input
then open other terminal and I execute the program in this way:
./program input output
and when the program is blocked on writeLine(fdOut, string, strlen(string)); ( because there isn't reader on output fifo) open other terminal and I do : cat output
and the I get(based on those input):
multiple
exit1
and I dont understand why.
should not wait until more input on input fifo?