A structure is a user defined data type in C/C++. A structure creates a data type that can be used to group items of possibly different types into a single type. How to create a structure? 'struct' keyword is used to create a structure. Using struct keyword: In C, we need to use struct to declare a struct variable. In C++, struct is not necessary. For example, let there be a structure for Record. In C, we must use “struct Record” for Record variables.