String is just like an array of elements of character (char) data type. Every valid string in c programming language must end with a NULL character or '\0'. ASCII value of a NULL character is 48. Without null character at the end, array is just an array of characters but not STRING.
C Strings and Character Arrays
C language provide 'char' data type to hold Alphabets and Special characters. Size of a single character is 1 Byte.