Add a program that adds numbers from the command line

02_command_line_tool/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: 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

02_command_line_tool/README.md

+# Basic Input
+
+If you want to pass arguments to your program, you can add them to `main`.

02_command_line_tool/add_integers.c

+#include <stdio.h>
+#include <stdlib.h>
+
+// To accept command line input, we add two arguments to main. The first will contain the number of
+// inputs on the command line, and the second is an array of C strings (pointers to characters) that
+// contain what was written. Main is special and has to take no arguments, or these two arguments.
+// (Other functions can take whatever arguments they like.)
+int main(int argc, const char* argv[]) {
+    // If the user didn't give us two numbers, we exit.
+    if (argc < 3) {
+        printf("Please type two numbers.\n");
+        return 0;
+    }
+
+    // If the user gave us more than two numbers, we just ignore the rest.
+    // Can you change the program so it adds all the numbers?
+    if (argc > 3) {
+        printf("Woah, there, that's a lot of numbers.\n");
+    }
+
+    int a = atoi(argv[1]);
+    int b = atoi(argv[2]);
+    int c = a + b;
+
+    printf("%i + %i = %i\n", a, b, c);
+}

03_inputs_and_outputs/.gitignore

+add_integers