Problems with C file writing - c

Question

I have problems writing to file, this is the code:
#include <stdio.h>
int main(int argc,char* argv[])
{
if(argc!=2)
{
printf("\x1B[31mError::%s takes exactly one argument!\n\x1B[0m",argv[0]);
return 1;
}
char string[100];
FILE* file=fopen(argv[1],"w");
if(file==NULL)
{
printf("\x1B[31mFile is invalid!\x1B[0m\n");
return 1;
}
while(!feof(stdin))
{
scanf("%s",string);
fprintf(file,"%s\n",string);
}
fclose(file);
return 0;
}
it should take input with scanf and writing to the file until i enter the end of file character (ctrl+Z), when it's finished running,the file i opened is empty. This code structure is also suggested in the deitel & deitel book, Do you know what's wrong here?
Also, i would like to know how can i take a whole phrase with scanf instead of a single word each time.. if i do scanf("%[^\n]",string)
the program gets confused and as soon as i write something, it will go in a loop writing the same thing over and over, and the file will become like 1,7Gb large.. help!

Answer 1

when user will press ctrl+z your process(a.out) will receive signal no 20 internally and your process will be stopped but data will not be saved because program got terminated abnormally.
you can type man 7 signal on terminal and check the default action of ctrl+z. So now you need to modify ctrl+z by-default action ? how ? use signal() or sigaction().
whenever ctrl+z is pressed, jumps to isr() and there save the current process status using exit() system call. ctrl+z is signal no 20.
I did small modifications in your code.
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
void isr(int n)
{
if(n == 20)//if ctrl+z is pressed then condition will be true
{
printf("in isr :\n");
exit(0);//exit(0) is normal termination of process i.e it will save current process context
}
}
int main(int argc,char* argv[])
{
if(argc!=2)
{
printf("\x1B[31mError::%s takes exactly one argument!\n\x1B[0m",argv[0]);
return 1;
}
char string[100];
FILE* file=fopen(argv[1],"w");
if(file==NULL)
{
printf("\x1B[31mFile is invalid!\x1B[0m\n");
return 1;
}
while(!feof(stdin))
{
signal(20,isr);//when user presses ctrl+z it will jump to isr()
scanf("%s",string);
fprintf(file,"%s\n",string);
}
fclose(file);
return 0;
}
once go through man pages of signal() and exit().