How to extract numbers from string in c?

Question

Say I have a string like ab234cid*(s349*(20kd and I want to extract all the numbers 234, 349, 20, what should I do ?

Answer 1

Make a state machine that operates on one basic principle: is the current character a number.

• When transitioning from non-digit to digit, you initialize your current_number := number.
• when transitioning from digit to digit, you "shift" the new digit in:
  current_number := current_number * 10 + number;
• when transitioning from digit to non-digit, you output the current_number
• when from non-digit to non-digit, you do nothing.

Optimizations are possible.