Differences between C and MATLAB (Kevin Lynch)

(Clarification: Certainly MATLAB has underlying data types; see www.mathworks.... . In normal usage, however, the user does not have to explicitly declare a variable's data type, as is required in C.)
For more information, see nu32.org. This video is a supplement to the book "Embedded Computing and Mechatronics with the PIC32 Microcontroller," Lynch, Marchuk, and Elwin. It is part of Northwestern University's ME 333 Introduction to Mechatronics.
An even lower-level language than C is the assembly language for your processor, where there is typically one CPU operation per line of code. (Your compiler actually translates your C code into assembly code before it is converted into machine-level code.) If you're watching this video, though, there is a good chance you are more familiar with a high-level language.
L-comp: The data type of a variable must be defined before it is used in C. Why?