From 7ab9d75b405a3ab46bda5a232baa9e88f0c07d6a Mon Sep 17 00:00:00 2001
From: Erik Strand <erik.strand@cba.mit.edu>
Date: Wed, 21 Oct 2020 00:09:09 -0400
Subject: [PATCH] Add a demo of different control structures
---
02_control_structures/Makefile | 19 +++++
02_control_structures/loops.c | 72 +++++++++++++++++++
.../Makefile | 2 -
.../README.md | 0
.../add_integers.c | 0
5 files changed, 91 insertions(+), 2 deletions(-)
create mode 100644 02_control_structures/Makefile
create mode 100644 02_control_structures/loops.c
rename {02_command_line_tool => 03_inputs_and_outputs}/Makefile (60%)
rename {02_command_line_tool => 03_inputs_and_outputs}/README.md (100%)
rename {02_command_line_tool => 03_inputs_and_outputs}/add_integers.c (100%)
diff --git a/02_control_structures/Makefile b/02_control_structures/Makefile
new file mode 100644
index 0000000..1d0e24c
--- /dev/null
+++ b/02_control_structures/Makefile
@@ -0,0 +1,19 @@
+# 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
diff --git a/02_control_structures/loops.c b/02_control_structures/loops.c
new file mode 100644
index 0000000..2e9710d
--- /dev/null
+++ b/02_control_structures/loops.c
@@ -0,0 +1,72 @@
+#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");
+ }
+}
diff --git a/02_command_line_tool/Makefile b/03_inputs_and_outputs/Makefile
similarity index 60%
rename from 02_command_line_tool/Makefile
rename to 03_inputs_and_outputs/Makefile
index 34690ff..f682fac 100644
--- a/02_command_line_tool/Makefile
+++ b/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
diff --git a/02_command_line_tool/README.md b/03_inputs_and_outputs/README.md
similarity index 100%
rename from 02_command_line_tool/README.md
rename to 03_inputs_and_outputs/README.md
diff --git a/02_command_line_tool/add_integers.c b/03_inputs_and_outputs/add_integers.c
similarity index 100%
rename from 02_command_line_tool/add_integers.c
rename to 03_inputs_and_outputs/add_integers.c
--
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