beginner in C under linux. write function doesn't work properly - c

Question

I'm trying to write a C program, that make user able to write stuff in a file. My Problem is that after making and running the program the file stay empty ?? any idea how can I solve this.
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
// the user should give a file to write the file
int main (int argc , char**argv)
{
int fd; // file descriptor
char ret; // the character
int offset;
if(argc != 2) {
printf("You have to give the name or the path of the file to work with \n");
printf("Exiting the program \n")
return -1;
}
fd = open (argv[1], O_WRONLY/*write*/|O_CREAT/*create if not found */, S_IRUSR|S_IWUSR/*user can read and write*/);
if (fd == -1) {
printf("can'T open the file ");
return -1;
}
printf("At wich position you want to start ");
scanf("%d",&offset);
lseek(fd,offset,SEEK_SET);
while(1) {
ret = getchar();
if(ret == '1') {
printf("closing the file");
close (fd);
return 1;
}
else
write (fd,red, sizeof(char));
}
return 0;
}
thanks in advance for you help.

Answer 1

I have made some changes,this should work:
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
int main (int argc , char**argv)
{
int fd; // file descriptor
char ret; // the character
int offset;
if(argc != 2){
printf("You have to give the name or the path of the file to work with \n");
printf("Exiting the program \n"); **//There was ';' missing here**
return -1;
}
fd = open (argv[1], O_WRONLY|O_CREAT,S_IRUSR|S_IWUSR);
if (fd == -1) {
printf("can'T open the file ");
return -1;
}
printf("At wich position you want to start ");
scanf("%d",&offset);
lseek(fd,offset,SEEK_SET);
while(1){
ret = getchar();
if(ret == '1'){
printf("closing the file");
close (fd);
return 1;
}
else
write (fd,&ret, sizeof(char)); **//red has been changed to &ret**
}
return 0;
}

Answer 2

One error I can notice, the call of write function:
write (fd,red, sizeof(char));
should be:
write (fd, &red, sizeof(char));
You forgot & before red, write need address.
syntax of write: int write( int handle, void *buffer, int nbyte );
This will cause an undefined behavior in your code at run time
Edit: in write function you are using red that is not defined, I think it should be ret variable in your code. correct it as write (fd, &ret, sizeof(char));
second, you forgot ; after printf("Exiting the program \n") in if, but I also think its mistake while posting question as you says you are getting run time error.
side note: If you are using gcc compiler then you can use gcc -Wall -pedantic to generate warnings

Answer 3

It should be:
write (fd,&ret, sizeof(char));
write takes the pointer to the memory position, and since ret is a single char, you need to pass a pointer to it.