add files

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.10)
+project(Calculator VERSION 1.0 LANGUAGES C)
+
+set(CMAKE_C_STANDARD 11)
+set(CMAKE_C_STANDARD_REQUIRED ON)
+
+enable_testing()
+
+add_library(calculator src/calculator.c)
+target_include_directories(calculator PUBLIC include)
+
+add_executable(main src/calculator.c)
+target_include_directories(main PUBLIC include)
+
+add_executable(test_calculator tests/test_calculator.c)
+target_link_libraries(test_calculator calculator m)
+target_include_directories(test_calculator PRIVATE include)
+
+add_test(NAME CalculatorTests COMMAND test_calculator)
+
+install(TARGETS calculator main DESTINATION bin)
+install(FILES include/calculator.h DESTINATION include)

include/calculator.h

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+#ifndef CALCULATOR_H
+#define CALCULATOR_H
+
+int add(int a, int b);
+int subtract(int a, int b);
+int multiply(int a, int b);
+double divide(int a, int b);
+
+#endif

src/calculator.c

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+#include "calculator.h"
+
+int add(int a, int b) {
+    return a + b;
+}
+
+int subtract(int a, int b) {
+    return a - b;
+}
+
+int multiply(int a, int b) {
+    return a * b;
+}
+
+double divide(int a, int b) {
+    if (b == 0) {
+        return 0.0;
+    }
+    return (double)a / b;
+}
+EOF

tests/test_calculator.c

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+#include <stdio.h>
+#include <assert.h>
+#include <math.h>
+#include "calculator.h"
+
+void test_add() {
+    assert(add(2, 3) == 5);
+    assert(add(-1, 1) == 0);
+    assert(add(0, 0) == 0);
+    printf("test_add passed\n");
+}
+
+void test_subtract() {
+    assert(subtract(5, 3) == 2);
+    assert(subtract(1, 1) == 0);
+    assert(subtract(0, 5) == -5);
+    printf("test_subtract passed\n");
+}
+
+void test_multiply() {
+    assert(multiply(3, 4) == 12);
+    assert(multiply(0, 5) == 0);
+    assert(multiply(-2, 3) == -6);
+    printf("test_multiply passed\n");
+}
+
+void test_divide() {
+    assert(fabs(divide(10, 2) - 5.0) < 0.001);
+    assert(fabs(divide(7, 2) - 3.5) < 0.001);
+    assert(divide(5, 0) == 0.0);
+    printf("test_divide passed\n");
+}
+
+int main() {
+    printf("Running calculator tests...\n\n");
+    test_add();
+    test_subtract();
+    test_multiply();
+    test_divide();
+    printf("\nAll tests passed!\n");
+    return 0;
+}