Which of the following is not a valid C data type?

Concept

In C, a type name must either be defined by the language or introduced by the program through a declaration such as typedef. The standard arithmetic type family includes integer types and floating types.

Application

Among the given values, int, float, and char are standard C type specifiers. real is not a predefined C type name; a program may use it as a type name only after explicitly defining an alias such as typedef float real;. Therefore, the value that is not a built-in C data type is real.

Contrast

• int denotes a signed integer type for whole-number values.

• float denotes a floating type for finite-precision real-number approximations.

• real is an ordinary identifier unless the program declares it as a typedef name.

• char denotes the character-sized integer type; sizeof(char) is 1 byte.

Cross-check

A declaration such as int x;, float y;, or char c; uses a standard type specifier. By contrast, real z; requires a prior declaration such as typedef float real;, confirming that real is not predefined by C.