Difference between procedural programming and functional programming

Procedural:

• The output of a routine does not always have a direct correlation with the input.
• Everything is done in a specific order.
• Execution of a routine may have side effects.
• Tends to emphasize implementing solutions in a linear fashion.

Functional:

• Often recursive.
• Always returns the same output for a given input.
• Order of evaluation is usually undefined.
• Must be stateless. i.e. No operation can have side effects.
• Good fit for parallel execution
• Tends to emphasize a divide and conquer approach.
• May have the feature of Lazy Evaluation.