What is Payment Gateway integration?

A payment gateway can be defined as a third party service, which is a combination of hardware and software that provides an interface to the bank credit card processing network. The credit card information is collected and is transferred over the Internet to the credit card processors in the encrypted format for transaction purpose. Some well-known payment gateways are AuthorizeNet, Google Checkout, USAePay, Verisign and Paypal.

Integrations with php, PHP INTEGRATION , PAYMENT INTEGRATION.

Payment Gateway integration
1. Google Checkout Integration
2. paypal standard integration (https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/howto_html_landing)
3. paypal pro integration php (https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/howto_api_paymentspro)
4. Payflow Link () (https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/howto_gateway_payflow_link)
5. Payflow Pro (https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/howto_gateway_payflowpro)

PHP source in browser, show php code , show_source();

Show the source of the current file:
/* some code here */
show_source(__FILE__);