What is the difference between scalar types and aggregate types in C？

Question

I have read a book called "Pointers On C". In that book, there is a type called scalar types.

I know that arithmetic types and pointer types are collectively called scalar types, but I want to know what is the difference between scalar type and aggregate type and what occasion use them?

Answer 1

C11-§6.2.5 Types (p21):

Arithmetic types and pointer types are collectively called scalar types. Array and structure types are collectively called aggregate types.⁴⁶⁾

Scalar data types can hold only single data item while aggregate types can hold more than one data items.

int a;             //Scalar Type
char c;            //Scalar Type
float *p;          //Scalar Type
char str[10];      //Aggregate Type
struct s{
    int a;
    float b[5];
} ss;              //Aggregate Type

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_{46) Note that aggregate type does not include union type because an object with union type can only contain one member at a time.}