fatal error: 'openssl/ssl.h' file not found on Mac

Correcting the problem - 

First make sure Command Line tools are already installed. 

xcode-select --install

xcode-select: error: command line tools are already installed, use "Software Update" to install updates

using Brew to update openssl - 

sudo brew update

sudo brew install openssl

sudo brew link --force openssl

Adding curl library in C project in Xcode

Steps:

1. Click over the project name in Xcode.

2. Go to "Build Phases" and expand "Link Binary with Libraries".

3. Click "+" sign and "Add Other". 

4. Click "Shift" + "Command" + "G". This will launch a folder select dialogue.

5. Go to "/usr/lib" and then select "libcurl.dylib".