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#include <stdio.h>
#include <stdlib.h>	/* strtol() */
#include <limits.h>	/* INT_MIN, INT_MAX */

/*********************************************************//**
 * @brief	Read into existing cstring s up to (ssize-1) chars from stdin or until
 *		ENTER is pressed, and null terminate it (removing ENTER if necessary).
 * 		If more than (len-1) chars have been typed before the ENTER is pressed,
 *		they are ignored and they are removed from the stdin buffer.
 *
 * @return	A pointer to the start of read s, or NULL on error.
 *************************************************************
 */
char *s_getsflushed( char *s, const size_t ssize )
{
	const size_t 	charsize = sizeof(char);/* don't assume 1 byte == sizeof(char) */
	size_t 		i = 0;
	

	/* sanity checks */
	if ( !s )
		return NULL;
	if ( ssize < charsize ) 
		return s;

	/* read chars from stdin */
	for (i=0; (s[i]=getc(stdin)) != '\n' && i < ssize-charsize; i += charsize)
		;					/* ... empty loop-body        */

	if ( s[i] != '\n' ) {				/* ssize reached without '\n'   */
		s[i] = '\0';				/* ... null terminate s       */
		while (getchar() != '\n')		/* ... flush remaining chars  */
			;				/* ... ... empty loop-body    */
	}
	else
		s[i] = '\0';

	return s;
}
/*********************************************************//**
 * @brief	Read safely an integer form stdin.
 * @return	The integer, or INT_MIN if input contained non-digits (including blanks),
 *		or INT_MAX in case of out of range integer value.
 *************************************************************
 */
int readInt( void )
{
	char input[ 255+1 ] = {'\0'};
	char *tail = NULL;
	long int ret = INT_MAX;			/* INT_MAX & INT_MIN denote errors (see comments above) */

	/* input failure? */
	if ( !s_getsflushed(input, 255+1) )
		return INT_MAX;

	ret = strtol(input, &tail, 10 );

	/* blank or non-digit chars in input? */
	if ( '\0' != *tail || (tail == input && 0 == ret) )
		return INT_MIN;

	/* over/underflowed input? */
	if ( ret > INT_MAX-1 || ret < INT_MIN+1 )
		return INT_MAX;

	/* everything ok */
	return (int)ret;
}

/* ------------------------------------------------- */
int main( void )
{
	int n;

	printf( "Enter a valid integer: " );
	n = readInt();

	if ( INT_MAX == n )
		puts("*** error: out of range integer!");
	else if ( INT_MIN == n )
		puts("*** error: blank or non-digit chars in input!");
	else
		printf( "%d was a valid input\n", n );

system("pause");	/* windows only */
	return 0;
}