What is the function in c for built a string.

Answer 1

Ok, but you should not be using gets() for input. it has no size arguments. The string buffer can be overrun if user enters string larger than your string size.
gets() is so bad that they deprecated it in C99 and removed it from C11 standard.

its better to use fgets(s, sizeof(s), stdin) for string input ,it will not write past your string size.

for strings scanf() has same problem as gets() if you do not give it input range:
scanf("%19s", s);

Answer 2

No function use charecter array..
char s[100];
you can store in this a string..
Or
by taking string input, you can store like
Syntax:
fgets(char_array, max_size_of_input, input_console) ;
Ex:
fgets(s, 100,stdin);
or gets(s) ; //simple way for a line of string.... But not recommended as it is dengerous..
scanf("%s", s); //for single word of string

Edit:
Martin Taylor oh. Yes I am not given that relating to char array of s but just a random example.... I added fgets later, but forget to check and edit..
Ok thank for that correction..
Actually, Iam for the questioner response.. What actually he looking,.. And to give a answer accordingly with clear examples of possible but I got no response and I forgot it.....