Question

C Language!

Please, comment what each line of code does in the code below and answer this question: (sentence is fine)

1. Aside from pressing ctrl-(d/z) at the beginning of a line causing the getnchar() function to return NULL, is there any way to enter less than 9 characters?

Code:

void exer1(void)
{
   char input[LEN];
   char *check;
getchar(); // Clearing character buffer.
printf("Please enter 9 characters: "); // Prompting the user to enter
// a specific input.
  
   check = getnchar(input, LEN - 1);
   if (check == NULL)
       puts("Input failed.");
   else
       puts(input);
   puts("Done.\n");

}

char * getnchar(char * str, int n)
{
   int i;
   int ch;

   for (i = 0; i < n; i++)
   {
       ch = getchar();
       if (ch != EOF)
           str[i] = ch;
       else
           break;
   }
   if (ch == EOF)
       return NULL;
   else
   {
       str[i] = '\0';
       return str;
   }
}

Answer 1

The code is given below which is properly commented line by line:

void exer1(void)
{
char input[LEN];/* input char array of size of LEN*/
char *check;/* pointer to char*/
getchar(); // Clearing character buffer.
printf("Please enter 9 characters: "); // Prompting the user to enter
// a specific input.
  
check = getnchar(input, LEN - 1);/* call to getnchar()*/
if (check == NULL)/* if NULL is in check*/
puts("Input failed.");/* message to display*/
else
puts(input);/* Display what is in input array */
puts("Done.\n");/*message to display*/

}
char * getnchar(char * str, int n)/* 'str' as a pointer to char array and 'n' as length*/
{
int i;/* integer variable declaration*/
int ch;/*char variable declaration*/

  
for (i = 0; i < n; i++)/*loops as long as value of i is less than n */
{
ch = getchar();/* reads a single char*/


if (ch != EOF)/* check to see if EOF generated by ctrl+d/z is not in char ch */


str[i] = ch; /* stores that character in str array at index i*/
else
break; /* breaks from loop if the character read is EOF generated by ctrl+d/z */
}
  
  
if (ch == EOF)/* check to see if EOF generated by ctrl+d/z is in char ch */

return NULL; /*returns NULL when ctrl+d/z pressed at beginning*/
else
{
str[i] = '\0';/* terminates the string str with string terminator char which is a '\0' */
return str; /*returns the str array*/
}
}

/**************************/
Aside from pressing ctrl-(d/z) at the beginning of a line causing the getnchar() function to return NULL, yes there is a way to enter less than 9 chars: just press ENTER key at beginning or when finished typing.

A complete modified code for this purpose with proper execution is given below:

/*
* File: main.c
*
*/

#include <stdio.h>
#include <stdlib.h>
#define LEN 10
/*
*
*/

void exer1(void); /*prototype declaration*/
char * getnchar(char * str, int n);/*prototype declaration*/
/*main() definition*/
int main() {
exer1(); /*call to exer1()*/

return (0);/* return on successful exit*/
}
/* exer1() definition*/
void exer1(void)
{
char input[LEN];/* input char array of size of LEN*/
char *check;/* pointer to char*/
getchar(); // Clearing character buffer.
printf("Please enter 9 characters: "); // Prompting the user to enter
// a specific input.
  
check = getnchar(input, LEN - 1);/* call to getnchar()*/
if (check == NULL)/* if NULL is in check*/
puts("Input failed.");/* message to display*/
else
puts(input);/* Display what is in input array */
puts("Done.\n");/*message to display*/

}
/* getnchar() definition*/
char * getnchar(char * str, int n)/* 'str' as a pointer to char array and 'n' as length*/
{
int i;/* integer variable declaration*/
int ch;/*char variable declaration*/

  
for (i = 0; i < n; i++)/*loops as long as value of i is less than n */
{
ch = getchar();/* reads a single char*/
/* I've commented the below line*/
/*
if (ch != EOF)
*/
if (ch != '\n')/* modified code to check if the character read is not ENTER key pressed */
str[i] = ch; /* stores that character in str array at index i*/
else
break; /* breaks from loop if the character read is ENTER key pressed*/
}
/* I've commented the below line*/
/*
if (ch == EOF)
*/
if (ch =='\n'&& i==0)/* modified code to check if ENTER key pressed is detected at beginning*/
return NULL; /*returns NULL when ENTER key is pressed at beginning*/
else
{
str[i] = '\0';/* terminates the string str with string terminator char which is a '\0' */
return str; /*returns the str array*/
}
}
/***********************/

Source code screen shot is given below:

Output screen shot is given below: