lecture9-feb9 - Announcements Lecture 9 Assignment 2 Q&A...

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1 Announcements Lecture 9 • Assignment 2 – Q&A • Topics for today – more arrays 1D Counters Example #define ARRAY_SIZE 100 . . . int counters [ARRAY_SIZE]; /* declare array of counters */ int number, i; const int SENTINEL = 9999; scanf (“ %d” , & number); while (number ! = SENTINEL ) { /* increment the counter for that number, read the next number*/ counters [number - 1] = counters [number -1] + 1; scanf (“ %d” , & number); } /* output table of how many times each value (1-100) was input */ for (i =1; i <= ARRAY_SIZE ; i++) printf ("the counter for number %d is %d\n”, i, counters [i - 1]); . . . How would we verify the correctness of the input? Partially Filled Array • Arrays cannot grow after they have been allocated • You can allocate more space (i.e. extra) than you believe your program will need • If you guess too low, you will still run out of space and terminate • You do not need to use all the elements in an array (but total computer memory is finite) You must keep track of the actual number of elements in a partially filled array Simple Array Algorithms Once you have an array with values in it there are a few common operations (and variants) that are often used in handling arrays Ordered Vs Unordered arrays - it depends int array1 [ ] = {22, 66, 31, 9, 77}; int array2 [ ] = {5, 10, 22, 32, 48, 66, 81, 92}; /* ordered */ – Counting the number of values – Finding a given value – Removing a value – Inserting a value Sorting an unordered array into an ordered array – Improves search performance Examples use a partially filled array of a class’s hypothetical scores on the first exam – each exam score is an integer from 0-100 /* program to find out how many students did not pass exam 1 */ #define CLASS_SIZE 142; /* allows for reuse next year */ . . . int exam1scores [CLASS_SIZE];
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This note was uploaded on 01/24/2010 for the course EE 312 taught by Professor Shafer during the Spring '08 term at University of Texas at Austin.

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lecture9-feb9 - Announcements Lecture 9 Assignment 2 Q&A...

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