HTTP requests from Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Arduino HTTP GET request code?

Consider this Arduino sketch snippet that makes an HTTP GET request to a server and prints the response code. What will be printed to the Serial Monitor?

Arduino

WiFiClient client;
HTTPClient http;

void setup() {
  Serial.begin(115200);
  WiFi.begin("SSID", "PASSWORD");
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }
  http.begin(client, "http://example.com");
  int httpCode = http.GET();
  Serial.println(httpCode);
  http.end();
}

void loop() {}

A 200

B 0

C -1

D 404

💡 Hint

HTTP status code 200 means success. The code variable holds the HTTP response code.

The http.GET() function returns the HTTP status code from the server. If the request is successful, it returns 200. Other values indicate errors or no connection.

🧠 Conceptual

intermediate

Which Arduino library is used for making HTTP requests?

You want to send HTTP GET and POST requests from your Arduino sketch. Which library provides the HTTPClient class to do this?

A Ethernet.h

B WiFi.h

C SPI.h

D HTTPClient.h

💡 Hint

Look for the library that has 'HTTP' in its name and provides HTTP methods.

The HTTPClient class is part of the HTTPClient.h library, which simplifies HTTP requests on Arduino.

🔧 Debug

advanced

Why does this Arduino HTTP POST code fail to send data?

Examine the code below. It tries to send JSON data via HTTP POST but the server never receives it. What is the main reason for failure?

Arduino

WiFiClient client;
HTTPClient http;

void setup() {
  Serial.begin(115200);
  WiFi.begin("SSID", "PASSWORD");
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }
  http.begin(client, "http://example.com/api");
  http.addHeader("Content-Type", "application/json");
  int httpCode = http.POST("{\"temp\": 25}");
  Serial.println(httpCode);
  http.end();
}

void loop() {}

A The HTTPClient.begin() is called with WiFiClient instead of WiFiClientSecure

B The WiFi connection is not established before the POST call

C The Content-Type header is missing

D The JSON string is not properly escaped

💡 Hint

Check the WiFi connection status before making HTTP requests.

If WiFi is not connected, HTTP requests will fail. The code waits for connection, so this is unlikely. But if the wait loop is skipped or WiFi fails, POST will fail.

📝 Syntax

advanced

Which option fixes the syntax error in this Arduino HTTP GET snippet?

Find the option that corrects the syntax error in this code snippet:

http.begin(client, "http://example.com")
int code = http.GET()
Serial.println(code)

A Change http.GET() to http.get()

B Remove parentheses from http.GET

C Add semicolons at the end of each line

D Replace double quotes with single quotes

💡 Hint

Arduino C++ requires statement terminators.

Each statement in Arduino C++ must end with a semicolon. Missing semicolons cause syntax errors.

🚀 Application

expert

How many bytes are sent in this Arduino HTTP POST request?

Given this Arduino code sending a JSON payload via HTTP POST, how many bytes are sent in the request body?

String payload = "{\"sensor\":\"temp\",\"value\":23}";
http.begin(client, "http://example.com/data");
http.addHeader("Content-Type", "application/json");
int code = http.POST(payload);
http.end();

A 28 bytes

B 26 bytes

C 30 bytes

D 24 bytes

💡 Hint

Count all characters including quotes and braces in the JSON string.

The payload string is exactly 28 characters long, so 28 bytes are sent in the POST body.