diff --git a/apps/calc.c b/apps/calc.c
new file mode 100644
index 0000000..b81091a
--- /dev/null
+++ b/apps/calc.c
@@ -0,0 +1,21 @@
+#include <calc.h>
+
+int add(int a, int b) {
+    return a + b;
+}
+
+int minus(int a, int b) {
+    return a - b;
+}
+
+int multiply(int a, int b) {
+    return a * b;
+}
+
+int divide(int a, int b) {
+    if (a != 0 && b != 0) {
+        return a / b;
+    } else {
+        return;
+    }
+}
diff --git a/apps/calc.h b/apps/calc.h
new file mode 100644
index 0000000..aba4e36
--- /dev/null
+++ b/apps/calc.h
@@ -0,0 +1,9 @@
+#ifndef CALC_H
+#define CALC_H
+
+int add(int a, int b);
+int minus(int a, int b);
+int multiply(int a, int b);
+int divide(int a, int b);
+
+#endif