1. 

Which of the following is not user defined data type?

1 : 
struct book
{
    char name[10];
    float price;
    int pages;
};
2 : 
long int l = 2.35;
3 : 
enum day {Sun, Mon, Tue, Wed};
A. 1
B. 2
C. 3
D. Both 1 and 2

Answer: Option B

Explanation:

C data types classification are

1. Primary data types

     1. int

     2. char

     3. float

     4. double

     5. void

2. Secondary data types (or) User-defined data type

     1. Array

     2. Pointer

     3. Structure

     4. Union

     5. Enum

So, clearly long int l = 2.35; is not User-defined data type.
(i.e.long int l = 2.35; is the answer.)