What are the signs that indicate a rotten subfloor and how can it be repaired effectively?

Signs of a rotten subfloor include sagging or uneven floors, soft spots, musty odors, and visible mold or mildew. To repair a rotten subfloor effectively, the damaged area should be cut out and replaced with new plywood or OSB. It's important to address the source of moisture that caused the rot to prevent future damage. Additionally, treating the area with a fungicide can help prevent mold growth.