#include <stdio.h>

#include <string.h>

#include <ctype.h>



// This is the function that makes the integer test

bool IsInteger( char *number )

{

   int len = strlen( number );

   bool isnumber = true;

   int i = 0;



   if( len == 0 || len > 9 ) // if the user did not enter an input

   {                         // or if the input is too big to be

	   return false;         // a "long" value.

   }



   while( i < len && isnumber ) // scanning the the input

   {

       if( isdigit( number[i] ) == 0 ) // check if there is a none digit character in the input

       {

            if( number[i] == '+' || number[i] == '-' ) // if so we verify if it is "+" or "-"

            {

                if(  i + 1 > len - 1 || i - 1 >= 0 ) // check the position of "+" or "-"

                {                                    // this signs could only be infront of

                   isnumber = false;                 // the number,no where else.

                }

            }

            if( number[i] != '+' && number[i] != '-' ) // if it's not "+" or "-" than

            {                                          // the expression is not a number

                isnumber = false;

            }

       }

       i++;

   }



   return isnumber;

}



void main()

{

    char number[20]; // buffer for storing number

    

    printf("Enter a number: "); // geting a number from the user

    gets(number);

    

	if( IsInteger( number ) == false ) // testing the input number

	{

       printf("This is not an integer.\nOr maybe this expression is too big "

	          "to be tested.\n");

	}

    else

	{

       printf("Thanks for entering an integer !\n");

	}