Question

I am new to Cstring, sorry for asking dumb question, please help.

char string[10];

printf("Give me your last name:\n");
scanf ("%s", string);                   //if i type 123 123
printf("Original string:%s\n", string);  //it shows 123

Compare to:

char string[] = "123 123";

printf("Original string:%s\n", string);  //it shows 123 123

Answer 1

This is the right behaviour. By default scanf reads the string until it reaches a whitespace.

From scanf manpage:

s
Matches a sequence of non-white-space characters;
the next pointer must be a pointer to character array that is long enough
to hold the input sequence and the terminating
null character (‘\0’), which is added automatically.
The input string stops at white space or at the maximum field width,
whichever occurs first.