Add a demo of different control structures

02_control_structures/Makefile

+# Change your compiler here if you're not using gcc. CC is for C, and CXX is for C++.
+CC = gcc
+CXX = g++
+
+CFLAGS = -Wall -O3
+
+.PHONY: all
+all: loops
+
+# Here I'm using some of Make's built in variables: $@ and $<. The former gets substituted with the
+# name of the target. In this case, that's "loops". The latter gets substituted with the first
+# prerequisite. In this case, that's "loops.c". These are hard to remember, but can save you some
+# typing if you decide to rename things.
+loops: loops.c
+	$(CC) $(CFLAGS) -o $@ $<
+
+.PHONY: clean
+clean:
+	rm loops

02_control_structures/loops.c

+#include <stdio.h>
+
+int main(void) {
+    // Here we declare an integer called i, and set it equal to zero.
+    int i = 0;
+
+    // This is a while loop. The code in the braces will run repeatedly as long as the condition is
+    // true. You don't actually need braces if there's only one statement (i.e. line). But it's not
+    // a bad habit to write them anyway, so that you don't accidentally skip anything. Unlike in
+    // Python, the indentation doesn't mean anything to the compiler -- it's just for you.
+    while (i < 5) {
+        printf("while loop: %i\n", i);
+        // This increments i. We could also use "i = i + 1" or "i += 1".
+        ++i;
+    }
+
+    // This is a for loop. It's like a while loop, but you name the iteration variable, state the
+    // loop condition, and write your increment statement (or whatever else you want to do at the
+    // end of each iteration) all up front.
+    for (int j = 0; j < 5; ++j) {
+        printf("for loop: %i\n", j);
+    }
+
+    // In C, 0 means false, but any other integer means true (usually we use 1). So this loop would
+    // run forever, except we we have a trick up our sleeve: you can exit the loop with the keyword
+    // "break". This works in for loops too.
+    i = 0;
+    while (1) {
+        printf("another while loop: %i\n", i);
+
+        if (i == 2) {
+            printf("leaving the while loop\n");
+            break;
+        }
+
+        ++i;
+    }
+
+    // Another useful loop keyword is "continue". It jumps to the next loop iteration early. Like
+    // "break", it works in for loops and while loops. Also note that we can reuse i here, like
+    // we've been doing in our while loops. Both loops work both ways, but it's more common to see
+    // for loops declare new variables.
+    for (i = 0; i < 5; ++i) {
+        // Here we use the modulo operator "%" to check if i is even.
+        if (i % 2 == 0) {
+            continue;
+        }
+
+        // This code only runs if i is odd.
+        printf("%i is odd\n", i);
+    }
+
+    // This is a switch statement. It's not a loop, but it is handy to dispatch to different pieces
+    // of code based on the value of some variable.
+    i = 42;
+    switch (i) {
+        case 0:
+            printf("i is 0\n");
+            break;
+        case 1:
+            printf("i is 1\n");
+            break;
+        case 2:
+            printf("i is 2\n");
+            break;
+        case 42:
+            printf("i is 42\n");
+            break;
+        default:
+            printf("i is something else\n");
+    }
+}

02_command_line_tool/Makefile → 03_inputs_and_outputs/Makefile

@@ -10,8 +10,6 @@ all: add_integers
 add_integers: add_integers.c
 	$(CC) $(CFLAGS) -o add_integers add_integers.c
 
-# This rule deletes all the binaries. It's declared "phony" which means it doesn't actually make
-# anything. Otherwise Make would get confused about when it should run this rule.
 .PHONY: clean
 clean:
 	rm add_integers