diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..f4bc5db
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+*.o
+calc
+case_*
+casegen
+out
\ No newline at end of file
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..e46d5d3
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,27 @@
+.PHONY: clean
+
+out: calc case_all
+	./calc < case_all > out
+
+case_all: case_add case_sub case_mul case_div
+	cat case_add case_sub case_mul case_div > case_all
+
+case_add: casegen
+	./casegen "add" 100 > case_add
+
+case_sub: casegen
+	./casegen "sub" 100 > case_sub
+
+case_mul: casegen	
+	./casegen "mul" 100 > case_mul
+
+case_div: casegen
+	./casegen "div" 100 > case_div
+
+calc: calc.c
+	gcc -o calc calc.c
+
+casegen: casegen.c
+	gcc -o casegen casegen.c
+clean:
+	rm -f out calc casegen case_* *.o
diff --git a/casegen.c b/casegen.c
new file mode 100644
index 0000000..6c736c8
--- /dev/null
+++ b/casegen.c
@@ -0,0 +1,48 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+const char *ops[] = {"add", "sub", "mul", "div"};
+
+uint32_t xrand() {
+	/* Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs" */
+	static uint32_t x = 2024;
+	x ^= x << 13;
+	x ^= x >> 17;
+	x ^= x << 5;
+	return x;
+}
+
+void help() {
+	printf("Usage: ./casegen <op> <num>\n"
+	       "Available <op>s: add, sub, mul, div.\n"
+	       "<num>: The number of test cases generated (a positive integer).\n");
+}
+
+int is_op_legal(char *op) {
+	size_t sz = sizeof(ops) / sizeof(ops[0]);
+	for (int i = 0; i < sz; i++) {
+		if (strcmp(op, ops[i]) == 0) {
+			return 1;
+		}
+	}
+	return 0;
+}
+
+int get_num(char *str_num, int *num) {
+	*num = strtol(str_num, NULL, 10);
+	return *num > 0;
+}
+
+int main(int argc, char **argv) {
+	int num;
+	if (argc != 3 || !is_op_legal(argv[1]) || !get_num(argv[2], &num)) {
+		help();
+		return 1;
+	}
+	while (num--) {
+		printf("%s %u %u\n", argv[1], xrand() % 10000 + 1, xrand() % 10000 + 1);
+	}
+	return 0;
+}
diff --git a/runbin b/runbin
new file mode 100644
index 0000000..0482405
Binary files /dev/null and b/runbin differ