C Programming Examples

• hello, world which also illustrates conditionals, variable declaration, and simple text I/O
• multifiles, an example illustrating breaking up a program into multiple source files, with header files and the #ifndef/#define/#endif idiom to prevent multiple inclusion.
• use_up_mem.c illustrating the declaration of pointer variables, dynamic memory allocation, and the perils of memory leaks (the program eventually halts when it runs out of memory). Note that the analogous program written in Java never runs out of memory, because the memory allocated in one pass through the loop becomes unusable on the next pass and is therefore automatically recycled.
• io.c illustrating the fgets function. Note that fgets takes an int parameter telling how large the buffer is; the simpler gets function doesn't, so if the user types something too long, it stomps over whatever happens to come next in memory, leading to nonsense variable values and/or crashing or freezing programs.
• file_io.c illustrating standard functions for reading from files (there are analogous functions to write to files)
• strcat_ex.c illustrating some common tasks with strings: concatenating strings, initializing strings, extracting parameters from the command line.
• array_ptr_0.c illustrating the differences among pointers to pointers, arrays of pointers, and arrays of arrays (i.e. multi-dimensional arrays). Note: changed 9/29/05
• struct_1.c illustrating the declaration and use of structs
• typedef_2.c illustrating making up new, convenient names for old, complicated types with typedef
• union_3.c illustrating union, a way of intentionally treating the same region of memory as two or more different types at different times. Dangerous, but can be useful.
• union_4.c illustrating unions with discriminator variables, so you can keep track of which type the object "really" is. Note: the language doesn't enforce this; the responsibility is entirely on the programmer.
• enum_5.c illustrating the use of enum to define groups of symbolic constants with distinct values (typically when you don't care what the values are).
• Pets, a miniature (but more realistic than multifiles) example of writing a program spread out over several source and header files.