Confusion on Malloc behavior, why it last input is not taken? - c

Question

This is a snippet of a program I am working on. I wanted to get information from the user, where the target variable cannot have predefined memory. For some reason my function does not work for the last section of the code. Any help will be appreciated.
Current Output:
Enter your name: Daniel
Hi Danie (expected as I put the limit to 5 characters)
Enter your phone number: 123456789
123456789
Enter your Note: (Here it breaks and does not print the contactNote variable.)
Here is the code:
char *getwords(int numberoftimes) {
char *words = malloc(sizeof(char));
int index = 0;
int character = EOF;
int size = 0;
int increase = 1;
int counter = 0;
char *temp;
while (character) {
character = getc(stdin);
if (numberoftimes == 0) {
if (character == '\n') {
character = 0;
}
} else if (counter == numberoftimes || character == '\n') {
character = 0;
}
if (size <= index) {
size += increase;
temp = realloc(words, size);
if (!temp) {
free(words);
words = NULL;
break;
}
words = temp;
}
words[index++] = character;
counter++;
}
return words;
}
int main() {
char *contactName, *contactNote;
long contactNumber;
printf("\nEnter your name: ");
char *getwords();
char *Name = getwords(5);
printf("\nHi %s\n", Name);
printf("\nEnter your phone number: ");
scanf("%lu", &contactNumber);
printf("\n%lu\n", contactNumber);
printf("\nEnter your Note: ");
char *getwords();
char *Note = getwords(0);
printf("\n%s\n", Note);
}

Answer 1

scanf() for the contact number leaves the ENTER sitting in the [keyboard] input buffer.
int main() {
char *contactName, *contactNote; // unused variables
long contactNumber;
printf("\nEnter your name: ");
char* getwords(); // unnecessary function declaration
char *Name = getwords(5);
printf("\nHi %s\n", Name);
printf("\nEnter your phone number: ");
scanf("%lu", &contactNumber); // leaves <ENTER> in buffer
printf("\n%lu\n", contactNumber);
printf("\nEnter your Note: ");
char* getwords(); // unnecessary function declaration
char *Note = getwords(0); // empty line because of previous <ENTER>
printf("\n%s\n", Note);
}
I suggest you also use getwords() for the number, then convert to long with strtol().

Answer 2

There are multiple problems in your code:
mixing getc() and scanf() is tricky as scanf() leaves the trailing newline pending in stdin so getc() reads this newline immediately. You should read all of your inputs with getwords().
the extra char *getwords(); declarations inside the body of main() are redundant and confusing.
getwords() is too complicated, especially for exiting the loop.
you do not always check for memory allocation error.
Here is a modified version:
#include <stdio.h>
#include <stdlib.h>
char *getwords(const char *prompt, int maxlen) {
char *words = malloc(sizeof(char));
int index = 0;
int size = 0;
char *temp;
if (words == NULL)
return NULL;
printf("%s", prompt);
for (;;) {
int character = getc(stdin);
if (character == EOF || character == '\n')
break;
if (index < maxlen) {
if (index >= size) {
size += 1;
temp = realloc(words, size + 1);
if (!temp) {
free(words);
return NULL;
}
words = temp;
}
words[index++] = character;
}
}
words[index] = '\0';
return words;
}
int main() {
char *Name = getwords("\nEnter your name: ", 5);
if (!Name)
return 1;
printf("\nHi %s\n", Name);
char *contact = getwords("\nEnter your phone number: ", 20);
if (!contact)
return 1;
long contactNumber = 0;
sscanf(contact, "%lu", &contactNumber);
printf("\n%lu\n", contactNumber);
char *Note = getwords("\nEnter your Note: ", 10);
if (!Note)
return 1;
printf("\n%s\n", Note);
return 0;
}