Write user input to a file and then read it - c

Question

I have to recieve user input with this style:
U word word2 word3
U word word2 word3
R word
R word
X
I want to write it to a file and then read what was written but the program is in a endless loop, and the file is being created but its empty, it seems to me the program never leaves the while loop that writes to a file for some reason.
void write_to_file(FILE *fp){
char buffer[37];
while(fgets(buffer, 37, stdin)){
fprintf(fp, "%s", buffer);
}
fclose(fp);
}
void read_from_file(FILE *fp){
char buffer[37];
char tipo;
char input_a[6];
char input_b[26];
while(fgets(buffer, 37, fp)) {
sscanf(buffer, "%c %s %[^\n]", &tipo, input_a, input_b);
switch(tipo) {
case 'U' :
// do stuff
break;
case 'R' :
// do stuff
break;
case 'X' :
exit(0);
break;
default :
printf("Invalid Operation\n");
}
}
}
int main(){
FILE *fp = fopen("input.txt","a+");
write_to_file(fp);
read_from_file(fp);
return 0;
}
I opened the file with a+ because in case the file already exists i want to write after the last line
Thanks in advance.

Answer 1

the program is in a endless loop ? Its because of below while() loop
while(fgets(buffer, 37, stdin)) {
}
As man 3 fgets says
fgets() return s on success, and NULL on error or when end
of file occurs while no characters have been read.
you can end this loop by hitting ctrl+d but if you press ctrl+d your main process a.out gets terminated. One way to solve this problem is give one extra \n or ENTER as input at last and then chen the return value of fgets().
Here is the sample code
void write_to_file(FILE *fp){
char buffer[37], *ptr = NULL;
while((ptr = fgets(buffer, 37, stdin))!=NULL) { /* It return NULL upon reaching EOF */
if(*ptr != '\n') { /* at last user enters \n, compare here, if true , break the loop */
fprintf(fp, "%s", buffer);
}
else
break;
}
fclose(fp);
}