CIS241

System-Level Programming and Utilities

C

Erik Fredericks, frederer@gvsu.edu
Fall 2025

Based on material provided by Erin Carrier, Austin Ferguson, and Katherine Bowers

But why?

• Help develop a better understanding of what high (and low) level langauges are doing!

• Understand memory management

  • i.e., Java/Python isn't handling it "for you"

• System programming - interact with OS

C vs. Java

Both are compiled, but to different things

• C: compiled to assembly language
• Java: compiled to Java bytecode (executed by JVM)
• Python: interpreted (unless if you're compiling to pyc)

Portability:

• Java: more portable

  • Bytecode executed by same JVM version on any machine

• C: less portable

  • Compiled code is architecture dependent

C vs. Java

Speed:

• C is generally faster than Java and Python
  • Java can be fast (JIT makes optimizations, Cython helps Python, etc.)

Compiled vs. Interpreted?

Compiled:

• C: gcc program.c
• Java: javac program.java

Interpreted (run without compiling)

• bash: bash script.sh
• Python: python program.py
• awk: gawk program.awk

Getting started with C

Hello world!

#include <stdio.h>

int main(void)
{
    printf("Hello world\n");
    return 0;
}

NOTE THE SEMI-COLONS!!!

C preprocessor

Performs source code substitution!

# indicates a preprocessing directive

include - replaces a line with contents of file

• Typically used for header files
• Essentially "importing"

define PI 3.14159

• Anywhere you have PI, replace with value
• Convention - use all caps

Running C code

Compiling:

• gcc program_file.c

  • Generates an a.out file

• gcc -o myprogram program_file.c

  • Generates a myprogram file

Running

• ./a.out
• ./myprogram

DON'T DO THIS

gcc -o project.c project.c

Why?

If you don't have a C compiler

(Including update/upgrade)

WSL (Ubuntu): sudo apt update && sudo apt upgrade && sudo apt install gcc

• (or more broadly, sudo apt install build-essential)

Potentially:
Mac (Homebrew):

• brew update
• brew upgrade
• brew info gcc
• brew install gcc
• brew cleanup
• https://discussions.apple.com/thread/8336714?sortBy=rank

Compiler flags!

• -o - specify output file
• -O - specify optimization level when compiling
  • Compiling goes to machine code
  • Some machine code is faster/uses less space (i.e., optimized)
  • Careful - high optimization levels can break code!
• -Wall - enables warning messages

https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

Sample O flags

• -O or -O1 means "optimize some"
• -O2 means "optimize more"
• -O3 means "optimize as much as possible"
• -Os and -Oz means "optimize for space"

C++?

C++ is an object-oriented version of C

• Not stricly an "extension"

C is procedural

If you know C, you can do C++ (with extra effort)

Why is it called C?

Wikipedia says:

A successor to the program language B.

https://en.wikipedia.org/wiki/C_(programming_language)

VSCode

The terminal is pretty easy but...

https://code.visualstudio.com/docs/languages/cpp