The concrete floor in a basement does nothing for the structural integrity of the house, so cracks in the floor are no real concern.
As for the foundation walls:
Zig-zag, step shaped cracks that follow the mortar joints of the blocks are common and caused by uneven settling of the house. Not ideal but typically not a concern.
Vertical crack lines are also caused by uneven settling and not of very high concern
Horizontal crack lines are caused by the wall caving inwards and are the most concerning type of crack. Sometimes the wall can be braced with steel beams after a crack has formed but usually it just delays the inevitable. The only real way to repair a horizontal crack is to dig out the wall and replace it.
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