Итог(общий вариант)

main.cpp

@@ -5,6 +5,7 @@
 #include "text.h"
 #include "svg.h"
 #include <curl/curl.h>
+#include <sstream>
 
 
 
@@ -16,6 +17,8 @@ struct Input {
 	size_t bin_count{};
 };
 
+
+
 Input
 input_data(istream& in, bool prompt = true){
 	size_t number_count;
@@ -40,13 +43,25 @@ input_data(istream& in, bool prompt = true){
 	return iiin;
 }
 
-int main(int argc, char* argv[]) {
+size_t
+write_data(void* items, size_t item_size, size_t item_count, void* ctx) {
+	stringstream* buffer = reinterpret_cast<stringstream*>(ctx);
+	size_t data_size = item_size * item_count;
+	buffer->write(reinterpret_cast<const char*>(items), data_size);
+
+	return data_size;
+}
+ 
+Input
+download(const string& address) {
+	stringstream buffer;
 
-	if (argc > 1) {
 	CURL* curl = curl_easy_init();
 	if (curl) {
 		CURLcode res;
-			curl_easy_setopt(curl, CURLOPT_URL, argv[1]);
+		curl_easy_setopt(curl, CURLOPT_URL, address.c_str());
+		curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
+		curl_easy_setopt(curl, CURLOPT_WRITEDATA, &buffer);
 		res = curl_easy_perform(curl);
 		if (res != CURLE_OK) {
 			cout << curl_easy_strerror(res);
@@ -54,9 +69,18 @@ int main(int argc, char* argv[]) {
 		}
 		curl_easy_cleanup(curl);
 	}
-		return 0;
+
+	return input_data(buffer, false);
+}
+
+int main(int argc, char* argv[]) {
+	Input in;
+	if (argc > 1) {
+		in = download(argv[1]);
+	}
+	else {
+		in = input_data(cin, true);
 	}
-	Input in = input_data(cin);
 	auto bins = make_histogram(in.numbers, in.bin_count);
 	show_histogram_svg(bins);
 	return 0;