added feature "add" as a skeleton to use for other features

src/add/add.c

@@ -0,0 +1,5 @@
+#include "add.h"
+
+int add(int a, int b) {
+    return a + b;
+}

src/add/add.h

@@ -0,0 +1,4 @@
+#ifndef SOME_H
+#define SOME_H
+int add(int a, int b);
+#endif

src/add/add_main.c

@@ -0,0 +1,10 @@
+#include "add.h"
+#include "../userinput.h"
+#include <stdio.h>
+
+int main() {
+    printf("add two numbers:\n");
+    int firstNum = getd("first number: ", NULL, NULL);
+    int secondNum = getd("second number: ", NULL, NULL);
+    printf("The result is: %d\n", add(firstNum, secondNum));
+}

test/add/test_add.c

@@ -0,0 +1,9 @@
+#include "unity.h"
+#include "add.h"
+
+void setUp(void){}
+void tearDown(void){}
+
+void test_add(void) {
+    TEST_ASSERT_EQUAL_INT(100, add(50, 50));
+}