Add ROT47 Example

README.md

@@ -8,7 +8,7 @@ This repository is intended as:
 * A interview‑prep playground
 * A reference for **concurrency, synchronization, low‑level and modern C++ techniques**
 * A growing set of **self‑contained, buildable examples**
-* A collection of more useful examples than leetcode puzzles.
+* A collection of more useful examples (and CLI tools) than leetcode puzzles.
 
 Examples include (and will expand to):
 
@@ -28,6 +28,8 @@ Examples include (and will expand to):
 * Performance‑oriented C++ idioms
 * Algorithms
     * [integer-factorization](./integer-factorization/)
+    * Encoding
+        * [rot47](./rot47/)
 * OOP
     * [virtual-interface](./virtual-interface/)
 

rot47/Makefile

@@ -0,0 +1,30 @@
+# pull in shared compiler settings
+include ../common.mk
+
+# per-example flags
+# CXXFLAGS += -pthread
+
+## get it from the folder name
+TARGET := $(notdir $(CURDIR))
+SRCS   := $(wildcard *.cpp)
+OBJS   := $(SRCS:.cpp=.o)
+
+all: $(TARGET)
+
+$(TARGET): $(OBJS)
+	$(CXX) $(CXXFLAGS) -o $@ $^
+
+%.o: %.cpp
+	$(CXX) $(CXXFLAGS) -c $< -o $@
+
+run: $(TARGET)
+	./$(TARGET) $(ARGS)
+
+clean:
+	rm -f $(OBJS) $(TARGET)
+
+# Delegates to top-level Makefile
+check-format:
+	$(MAKE) -f ../Makefile check-format DIR=$(CURDIR)
+
+.PHONY: all clean run check-format

rot47/main.cpp

@@ -0,0 +1,32 @@
+#include <iostream>
+#include <string>
+#include <string_view>
+#include <ranges>
+
+[[nodiscard]]
+std::string
+rot47(std::string_view input)
+{
+    auto transform = [](char c) { return (c >= 33 && c <= 126) ? static_cast<char>(33 + ((c - 33 + 47) % 94)) : c; };
+
+    std::string output;
+    output.reserve(input.size());
+
+    for (char c : input | std::views::transform(transform)) {
+        output.push_back(c);
+    }
+
+    return output;
+}
+
+int
+main(int argc, char* argv[])
+{
+    for (int i = 1; i < argc; ++i) {
+        std::cout << rot47(argv[i]);
+
+        if (i + 1 < argc) {
+            std::cout << ' ';
+        }
+    }
+}

rot47/tests.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+set -ex
+
+./rot47
+
+helloworld=$(./rot47 'w6==@ (@C=5P')
+
+if [ "$helloworld" != "Hello World!" ]; then
+    echo "Test failed: expected 'Hello World!' but got '$helloworld'"
+    exit 1
+fi