What are the differences between PHP 5 and PHP 7?

Here’s a table that outlines the key differences between PHP 5 and PHP 7:

Feature	PHP 5	PHP 7
Performance	Slower execution and memory usage.	Significantly faster with optimized memory usage (up to 2x faster).
Type Declarations	Limited to type hinting for arrays and objects.	Supports scalar type declarations for `int`, `float`, `string`, and `bool`.
Return Type Declarations	Not available.	Introduced return type declarations for functions and methods.
Error Handling	Errors (e.g., fatal errors) halt execution and are not recoverable.	Introduced the `Engine Exceptions` system, enabling better error handling using `\Throwable`.
Spaceship Operator (`<=>`)	Not available.	Introduced for combined comparison of two expressions (`x <=> y`).
Null Coalescing Operator (`??`)	Not available.	Introduced for shorthand null checks (`$x = $a ?? $b`).
Anonymous Classes	Not supported.	Introduced support for creating anonymous classes.
New Operators	No new operators in PHP 5.	Introduced operators like `null coalescing` (`??`) and `spaceship` (`<=>`).
Uniform Variable Syntax	Not consistent; could be confusing in complex variable references.	Improved, providing consistent behavior for variable references.
Memory Usage	Higher memory consumption.	Reduced memory usage through optimized memory management.
`E_STRICT` Error Reporting	`E_STRICT` was a separate error level.	`E_STRICT` errors are included in `E_ALL` in PHP 7.
Deprecated Items	Certain functions (e.g., `mysql_*`) were deprecated but still used.	Fully removed deprecated functions (e.g., `mysql_*` functions).
Unicode Codepoint Escape	Not available.	Added support for `\u{}` escape syntax for Unicode codepoints.
Scalar Type Hints	Not available.	Allows type hints for scalar values (`int`, `string`, `bool`, etc.).
Fatal Error Handling	Fatal errors halted execution without recoverability.	Fatal errors now throw `EngineException`, making it easier to handle.
Consistent 64-bit Support	64-bit support inconsistent across platforms.	Consistent 64-bit support on all platforms, including Windows.
Integer Division	No dedicated function for integer division.	Introduced `intdiv()` function for integer division.
Anonymous Function Support	Supported but no anonymous class support.	Supported with the addition of anonymous classes.
Extensions	Some older extensions were bundled with core PHP.	Some old and rarely used extensions removed for optimization.
Backward Compatibility	More backward compatibility for older codebases.	Some breaking changes in compatibility with older PHP 5 code.
New Reserved Keywords	No new reserved keywords introduced.	Introduced new reserved keywords like `int`, `float`, `bool`, `string`, etc.
Consistent Error Handling for `foreach`	Some inconsistencies when modifying arrays within a loop.	Improved consistency when modifying arrays during `foreach` loops.
PHPNG (PHP Next-Gen Engine)	Not implemented.	Introduced a new Zend Engine (PHPNG) for improved performance.

Summary:

PHP 7 offers significant performance improvements, better memory management, and enhanced error handling.
It introduces modern programming features like type declarations, return type hints, new operators, and anonymous classes.
Deprecated features were completely removed, making PHP 7 more efficient and secure.

This makes PHP 7 a more powerful and performance-oriented language compared to PHP 5.

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