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Arrays

Arrays. Real-world Scenario. PLU code is missing for a product you are buying at the grocery counter. Associate may use a cheat sheet showing PLU code for each product – it works like an array. Historical snippets …. BASIC & FORTRAN : array index started at 1 COBOL?

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Arrays

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  1. Arrays

  2. Real-world Scenario • PLU code is missing for a product you are buying at the grocery counter. • Associate may use a cheat sheet showing PLU code for each product – it works like an array.

  3. Historical snippets … • BASIC & FORTRAN : array index started at 1 • COBOL? • Modern languages use index starting at 0 • How about Visual Basic?

  4. Array index start with 0 or 1? "Should array indices start at 0 or 1? My compromise of 0.5 was rejected without, I thought, proper consideration." -- Stan Kelly-Bootle

  5. Array index start with 0 or 1?

  6. Scenario: Max price • Let us say we want to read list of prices from the user and find the max price. • Do we need an array?

  7. Find max price: pseudocode item_number = 0 DOWHILE not eof item_number = item_number + 1 read item_price[item_number] ENDDO max_price_item = 0 max_price = 0.00 FOR i = 1 to item_number do IF max_price < item_price[i ] THEN max_price_item = i; max_price = item_price[i ]; ENDIF ENDFOR print max_price_item, max_price

  8. Find max price: no arrays item_number = 0 max_price_item = 0 max_price = 0.00 DOWHILE not eof item_number = item_number + 1 read item_price IF max_price < item_price THEN max_price_item = i; max_price = item_price; ENDIF ENDDO print max_price_item, max_price

  9. When arrays are needed? • Only if we are going to use all those individual input values again.

  10. Do we need arrays? • Mortgage amortization table expansion – show the output for user-specified year

  11. Do we need arrays? • Compute total ticket sales/donations for the day

  12. Do we need arrays? • Find max, min, average air-fare paid by customers

  13. Do we need arrays? • Find the median air-fare paid by customers

  14. Do we need arrays? • Output all the airfare amounts in sorted order

  15. Do we need arrays? • Keeping track of your score at Golf course

  16. Arrays • Easy access • Fixed size • When bigger size is needed, we need to allocate new array and copy the current contents over. • Use ArrayList for varying array sizes (not covered in this course)

  17. Multi-dimensional arrays • Students’ scores in one assignment intscores[student_index]

  18. Multi-dimensional arrays • Students’ scores in all assignments int scores[assignment_index][student_index]

  19. Multi-dimensional arrays • Students’ scores in all assignments for several sessions of that course int scores[session_index][assignment_index][student_index]

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