Which of the following correctly defines an integer variable 'i' in C++?

The correct statement for defining an integer variable 'i' in C++ is the first choice, which uses the 'int' data type. In C++, the 'int' type is specifically designed to hold integer values, which are whole numbers without any fractional or decimal component. When you declare 'int i = 0;', you are initializing the variable 'i' to zero, effectively allocating memory for it and setting its value at the same time.

The other options involve different data types. The 'float' type is used for representing single-precision floating-point numbers, which can hold decimal values. The 'double' type allows for double-precision floating-point numbers, which also includes decimal representation and can represent a much larger range of values. The 'char' type is for storing single characters and is not suitable for representing integers. Each of these data types serves specific purposes and cannot be used interchangeably with integers, which is why they are not appropriate for this task.