Which of the following data types is NOT considered primitive in C?

In C, primitive data types are the basic types that are built into the language and represent single values. These include types such as char (for character values), int (for integer values), and double (for floating-point values with double precision). Each of these types is fundamental to C programming and can be directly manipulated by the language and the compiler without the need for any additional constructs.

In contrast, String is not a primitive data type in C. Instead, strings in C are treated as arrays of characters terminated by a null character (often denoted as '\0'). This means that working with strings requires additional handling, such as managing memory for dynamic length and using standard library functions (strcpy, strlen, etc.) to manipulate them. Therefore, in the context of this question, String stands out as the data type that is not inherently primitive within the C language.