Thread: new problem after not using fflush(stdin)

This is my previous codes:

Code:

	printf("Please key in Sales Agent's code number>");/* Output statement*/
    scanf("%d", &num);
	fflush(stdin);

	while( !(num >= 1000 && num <= 9999) )/*if the condition is not true then print the error message*/
	{
		printf("\aInvalid code number! Please key in 4 digits code number.\n");
		main();
	}

After changing fflush(stdin) to if ( (scanf("%d",&num) !=1)
when i input a alphabet for variable num it will cause the problem to do a infinity loop.

make me confusing .......
before that just a single line code... Yet....
Any other simple way?....
i canT understand the codes ...