Preprocessor
Early C had neither constant declarations nor type declarations, and the C language was originally defined as needing a "preprocessor"; a separate program, and pass, that handled constant, include and macro definitions, to keep memory usage down. Later, with ANSI C, it obtained constant and type definitions features and the preprocessor also became part of the language itself, leading to the syntax we see today.
Pascal constant and type defines are built in, but there were programmers using a preprocessor also with Pascal (sometimes the same one used with C), certainly not as common as with C. Although often pointed out as a "lack" in Pascal, technically C doesn't have program modularity nor macros built in either. It has a simple low level separate compilation facility, however (traditionally using the same generic linker used for assembly language), Pascal does not.
Read more about this topic: Comparison Of Pascal And C