main.c

#include <stdio.h>
#include "util.h"

int main(void) {
  int a = 99;
  int b = 100;

  printf("MAX: %d\n", max(a,b));
  printf("MIN: %d\n", min(a,b));
  
  return 0;
}

Rakefile

require 'rake/clean'

CC = "gcc"

SRCS = FileList["**/*.c"]
OBJS = SRCS.ext('o')

CLEAN.include(OBJS)
CLOBBER.include("main")

task :default => "main"

file "main" => OBJS do |t|
  sh "#{CC} -o #{t.name} #{t.prerequisites.join(' ')}"
end

rule '.o' => '.c' do |t|
  sh "#{CC} -c #{t.source}"
end

util.c

#include "util.h"
int max(int a, int b) {
  if (a >= b) {
    return a;
  }
  return b;
}

int min(int a, int b) {
  if (a <= b) {
    return a;
  }
  return b;
}

util.h

int max(int a, int b);
int min(int a, int b);