code:

.gitignore

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+bin/
+obj/

histogram.cpp

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+#include "histogram.h"
+#include <vector>
+
+void
+find_minmax(const std::vector<double>& numbers, double& min, double& max) {
+    min = numbers[0];
+    max = numbers[0];
+
+    for (double x : numbers) {
+        if (x < min) {
+            min = x;
+        } else if (x > max) {
+            max = x;
+        }
+    }
+}
+
+std::vector<size_t>
+make_histogram(const std::vector<double>& numbers, size_t bin_count) {
+    std::vector<size_t> bins(bin_count, 0);
+
+    double min, max;
+    find_minmax(numbers, min, max);
+
+    double bin_size = (max - min) / bin_count;
+    if (bin_size == 0) {
+        bin_size = 1;
+    }
+
+    for (size_t i = 0; i < numbers.size(); i++) {
+        bool found = false;
+        for (size_t j = 0; (j < bin_count - 1) && !found; j++) {
+            auto lo = min + j * bin_size;
+            auto hi = min + (j + 1) * bin_size;
+            if ((lo <= numbers[i]) && (numbers[i] < hi)) {
+                bins[j]++;
+                found = true;
+            }
+        }
+        if (!found) {
+            bins[bin_count - 1]++;
+        }
+    }
+
+    return bins;
+}

histogram.h

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+#ifndef HISTOGRAM_H_INCLUDED
+#define HISTOGRAM_H_INCLUDED
+
+#include <vector>
+
+std::vector<size_t>
+make_histogram(const std::vector<double>& numbers, size_t bin_count);
+
+#endif // HISTOGRAM_H_INCLUDED

histogram_internal.h

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+#ifndef HISTOGRAM_INTERNAL_H_INCLUDED
+#define HISTOGRAM_INTERNAL_H_INCLUDED
+
+#include <vector>
+
+void find_minmax(const std::vector<double>& numbers, double& min, double& max);
+
+#endif // HISTOGRAM_INTERNAL_H_INCLUDED

lab01.cbp

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+<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
+<CodeBlocks_project_file>
+	<FileVersion major="1" minor="6" />
+	<Project>
+		<Option title="lab01" />
+		<Option pch_mode="2" />
+		<Option compiler="gcc" />
+		<Build>
+			<Target title="Debug">
+				<Option output="bin/Debug/lab01" prefix_auto="1" extension_auto="1" />
+				<Option object_output="obj/Debug/" />
+				<Option type="1" />
+				<Option compiler="gcc" />
+				<Compiler>
+					<Add option="-g" />
+				</Compiler>
+			</Target>
+			<Target title="Release">
+				<Option output="bin/Release/lab01" prefix_auto="1" extension_auto="1" />
+				<Option object_output="obj/Release/" />
+				<Option type="1" />
+				<Option compiler="gcc" />
+				<Compiler>
+					<Add option="-O2" />
+				</Compiler>
+				<Linker>
+					<Add option="-s" />
+				</Linker>
+			</Target>
+		</Build>
+		<Compiler>
+			<Add option="-Wall" />
+			<Add option="-fexceptions" />
+		</Compiler>
+		<Unit filename="main.cpp" />
+		<Extensions>
+			<lib_finder disable_auto="1" />
+		</Extensions>
+	</Project>
+</CodeBlocks_project_file>

main.cpp

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+#include <iostream>
+#include <sstream>
+#include <string>
+#include <vector>
+#include <curl/curl.h>
+#include "histogram.h"
+#include "text.h"
+#include "svg.h"
+
+using namespace std;
+
+struct Input {
+    vector<double> numbers;
+    size_t bin_count{};
+};
+
+Input input_data(istream& in, bool prompt) {
+    if (prompt) {
+        cerr << "Enter number count, numbers and bin count: ";
+    }
+
+    size_t number_count;
+    in >> number_count;
+
+    Input input;
+    input.numbers.resize(number_count);
+
+    for (size_t i = 0; i < number_count; i++) {
+        in >> input.numbers[i];
+    }
+
+    in >> input.bin_count;
+
+    return input;
+}
+
+size_t write_data(void* items, size_t item_size, size_t item_count, void* ctx) {
+    size_t data_size = item_size * item_count;
+
+    stringstream* buffer = reinterpret_cast<stringstream*>(ctx);
+
+    buffer->write(reinterpret_cast<const char*>(items), data_size);
+
+    return data_size;
+}
+
+Input download(const string& address) {
+    stringstream buffer;
+
+    CURL* curl = curl_easy_init();
+    if (curl) {
+        curl_easy_setopt(curl, CURLOPT_URL, address.c_str());
+
+        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
+        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &buffer);
+
+        CURLcode res = curl_easy_perform(curl);
+        if (res != CURLE_OK) {
+            cerr << "cURL error: " << curl_easy_strerror(res) << endl;
+            curl_easy_cleanup(curl);
+            exit(1);
+        }
+
+        curl_easy_cleanup(curl);
+    } else {
+        cerr << "curl_easy_init() failed" << endl;
+        exit(1);
+    }
+
+    return input_data(buffer, false);
+}
+
+int main(int argc, char* argv[]) {
+    Input input;
+
+    if (argc > 1) {
+        input = download(argv[1]);
+    } else {
+        input = input_data(cin, true);
+    }
+
+    const auto bins = make_histogram(input.numbers, input.bin_count);
+    show_histogram_svg(bins);
+
+    return 0;
+}

svg.cpp

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+#include <iostream>
+#include <vector>
+#include <string>
+
+using namespace std;
+
+void svg_begin(double width, double height) {
+    cout << "<?xml version='1.0' encoding='UTF-8'?>\n";
+    cout << "<svg ";
+    cout << "width='" << width << "' ";
+    cout << "height='" << height << "' ";
+    cout << "viewBox='0 0 " << width << " " << height << "' ";
+    cout << "xmlns='http://www.w3.org/2000/svg'>\n";
+}
+
+void svg_end() {
+    cout << "</svg>\n";
+}
+
+void svg_text(double left, double baseline, const string& text) {
+    cout << "<text x='" << left << "' y='" << baseline << "'>" << text << "</text>\n";
+}
+
+void svg_rect(double x, double y, double width, double height,
+              string stroke = "black", string fill = "black") {
+    cout << "<rect x='" << x << "' y='" << y
+         << "' width='" << width << "' height='" << height
+         << "' stroke='" << stroke << "' fill='" << fill << "' />\n";
+}
+
+void show_histogram_svg(const vector<size_t>& bins) {
+    const auto IMAGE_WIDTH = 400;
+    const auto IMAGE_HEIGHT = 300;
+    const auto TEXT_LEFT = 20;
+    const auto TEXT_BASELINE = 20;
+    const auto TEXT_WIDTH = 50;
+    const auto BIN_HEIGHT = 30;
+
+    svg_begin(IMAGE_WIDTH, IMAGE_HEIGHT);
+
+    double top = 0;
+    size_t max_bin = 0;
+    for (size_t i = 0; i < bins.size(); ++i) {
+        if (bins[i] > max_bin) {
+            max_bin = bins[i];
+        }
+    }
+    double scale = (max_bin > 0) ? (IMAGE_WIDTH - TEXT_WIDTH) * 1.0 / max_bin : 0;
+
+    for (size_t bin : bins) {
+        const double bin_width = scale * bin;
+        svg_text(TEXT_LEFT, top + TEXT_BASELINE, to_string(bin));
+        svg_rect(TEXT_WIDTH, top, bin_width, BIN_HEIGHT);
+        top += BIN_HEIGHT;
+    }
+
+    svg_end();
+}

svg.h

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+#ifndef SVG_H_INCLUDED
+#define SVG_H_INCLUDED
+
+#include <vector>
+
+void svg_begin(double width, double height);
+void svg_end();
+void show_histogram_svg(const std::vector<size_t>& bins);
+
+#endif // SVG_H_INCLUDED

text.cpp

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+#include "text.h"
+#include <iostream>
+
+void
+show_histogram_text(const std::vector<size_t>& bins, size_t screen_width) {
+    const size_t MAX_ASTERISK = screen_width - 3 - 1;
+
+    size_t max_count = 0;
+    for (size_t count : bins) {
+        if (count > max_count) {
+            max_count = count;
+        }
+    }
+
+    for (size_t i = 0; i < bins.size(); i++) {
+        size_t height = 0;
+
+        if (max_count > MAX_ASTERISK) {
+            height = static_cast<size_t>(
+                MAX_ASTERISK * static_cast<double>(bins[i]) / max_count
+            );
+        } else {
+            height = bins[i];
+        }
+
+        if (bins[i] < 10) {
+            std::cout << "  " << bins[i] << "|";
+        } else if (bins[i] < 100) {
+            std::cout << " " << bins[i] << "|";
+        } else {
+            std::cout << bins[i] << "|";
+        }
+
+        for (size_t j = 0; j < height; j++) {
+            std::cout << "*";
+        }
+        std::cout << std::endl;
+    }
+}

text.h

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+#ifndef TEXT_H_INCLUDED
+#define TEXT_H_INCLUDED
+
+#include <vector>
+
+void show_histogram_text(const std::vector<size_t>& bins, size_t screen_width = 80);
+
+#endif // TEXT_H_INCLUDED

unittest.cbp

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+<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
+<CodeBlocks_project_file>
+	<FileVersion major="1" minor="6" />
+	<Project>
+		<Option title="unittest" />
+		<Option pch_mode="2" />
+		<Option compiler="gcc" />
+		<Build>
+			<Target title="Debug">
+				<Option output="bin/Debug/unittest" prefix_auto="1" extension_auto="1" />
+				<Option object_output="obj/Debug/" />
+				<Option type="1" />
+				<Option compiler="gcc" />
+				<Compiler>
+					<Add option="-g" />
+				</Compiler>
+			</Target>
+			<Target title="Release">
+				<Option output="bin/Release/unittest" prefix_auto="1" extension_auto="1" />
+				<Option object_output="obj/Release/" />
+				<Option type="1" />
+				<Option compiler="gcc" />
+				<Compiler>
+					<Add option="-O2" />
+				</Compiler>
+				<Linker>
+					<Add option="-s" />
+				</Linker>
+			</Target>
+		</Build>
+		<Compiler>
+			<Add option="-Wall" />
+		</Compiler>
+		<Extensions>
+			<lib_finder disable_auto="1" />
+		</Extensions>
+	</Project>
+</CodeBlocks_project_file>

unittest.cpp

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+#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
+#include "doctest.h"
+#include "histogram_internal.h"
+#include <vector>
+
+TEST_CASE("distinct positive numbers") {
+    double min = 0;
+    double max = 0;
+    find_minmax({1, 2}, min, max);
+    CHECK(min == 1);
+    CHECK(max == 2);
+}
+
+TEST_CASE("find_minmax with one element") {
+    std::vector<double> numbers{42};
+    double min, max;
+    find_minmax(numbers, min, max);
+    CHECK(min == 42);
+    CHECK(max == 42);
+}
+
+TEST_CASE("find_minmax with negative values") {
+    std::vector<double> numbers{-10.5, -2.3, -3.3};
+    double min, max;
+    find_minmax(numbers, min, max);
+    CHECK(min == -10.5);
+    CHECK(max == -2.3);
+}
+
+TEST_CASE("find_minmax with identical elements") {
+    std::vector<double> numbers{7, 7, 7, 7};
+    double min, max;
+    find_minmax(numbers, min, max);
+    CHECK(min == 7);
+    CHECK(max == 7);
+}