CSC 107 – Programming For Science

Today’s Goal  Become familiar with simple arrays  Declaring an array variable  Assigning data to array entries  Using values stored in an array  Know connection between arrays and loops

Variables  Variable  Variable name location to store data  Only for humans; 0 x 7E8A2410 harder to remember  Assignments update memory location with new value  Memory location updated by assignment ONLY  When variable is used in program…  …uses current value at that memory location  Variable can store only one value  Often want multiple values, like adjusting for interest

Adjusting For Interest  First call, computed result for every year  Then all but last year computed in second call  Third time we called function, computed all but last 3 … and so on…  Only adjusted for 1 year last time we called function  Interest rate, amount, and results were constant  Unless save in variables, we have to recompute  Using variables required knowing years when coding

Could Have Spent Time

Can Make Stronger, Bigger  Arrays  Arrays are variables that can hold many items  Creates range of locations in which to store data  Locations are numbered sequentially from 0 entries  Array entries like variables in their own right  To be able to use them, must declare array (& entries)  Value unknown until assigned in the program  But not a true variable, entries depend on array  Access only via array using the entry's index

Declaring Array Variables  Like all variables, must declare before use size  Type, name, & size needed for array declaration  Still variables, so names follow usual rules  Variable is array of the type, so use any legal type  Each of the array's entries hold value of that type  Size must be integer since ½ a value hard to use

Declaring Array Variables  Like all variables, must declare before use size  Type, name, & size needed for array declaration  Still variables, so names follow usual rules  Variable is array of the type, so use any legal type  Each of the array's entries hold value of that type  Size must be integer since ½ a value hard to use

Declaring Array Size

Initializing an Array

Legal Array Entries  Access array's entries indexed from 0 to size-1  0, 1, 2, 3, 4 legal if size of 5 used to declare array  Array created with size of 8: 0, 1, 2, 3, 4, 5, 6, 7 legal  0 only legal index if size declared as 1

Legal Array Entries

Guns (& C++) Don't Kill  C++ make arrays easy, but mistakes easy also  Code can access any index within an array int  No problems compiling, as long as index an int  Includes indices like -1 or that stupid  To find size, could try using sizeof( array variable )  Entry outside array bounds accessed by program  Program may crash with “Segmentation Fault”  Other variable's value used and updated  Program may be able to complete normally

Using An Array  Each array entry behaves like variable  Accessed via array variable is only difference  To use or assign entry, specify index inside brackets  Example code snippet computing powers of 2: long loserArray[10]; loserArray[0] = 1; for (long i=0; i < sizeof(loserArray);i++){ loserArray[i] = loserArray[i-1] * 2; cout << loserArray[i] << endl; }

Using An Array  Each array entry behaves like variable  Accessed via array variable is only difference  To use or assign entry, specify index inside brackets  Example code snippet computing powers of 2: long loserArray[10]; loserArray[0] = 1; for (long i=0; i < sizeof(loserArray);i++){ loserArray[i] = loserArray[i-1] * 2; cout << loserArray[i] << endl; }

Using An Array  Each array entry behaves like variable  Accessed via array variable is only difference  To use or assign entry, specify index inside brackets  Example code snippet computing powers of 2: long loserArray[10]; loserArray[0] = 1; for (int i=0; i < sizeof(loserArray); i++){ loserArray[i] = loserArray[i-1] * 2; cout << loserArray[i] << endl; }

Using An Array  Each array entry behaves like variable  Accessed via array variable is only difference  To use or assign entry, specify index inside brackets  Example code snippet computing powers of 2: const int BORED_NOW = 10; long loserArray[BORED_NOW]; loserArray[0] = 1; for (int i=0; i < BORED_NOW; i++){ loserArray[i] = loserArray[i-1] * 2; cout << loserArray[i] << endl; }

Let's Trace This Code int main() { const int BORED_NOW = 4; long loserArray[BORED_NOW]; loserArray[0] = 1; for (int i=1; i < BORED_NOW; i++){ loserArray[i] = loserArray[i-1] * 2; cout << loserArray[i] << endl; } cout << "Sorry its stupid!" << endl; return 0; }

Your Turn  Get into your groups and try this assignment

For Midterm  You can use on this midterm:  Your textbook & notes IF  Printout of slides IF has notes on that day's slides  At the same time, you may NOT use:  Computer, calculator, cell phone, or similar  Copies of daily activities and/or solutions  Friends, Romans, countrymen or their ears  To be certain rules are followed, when test ends  Hand in all printed material you had with you

How to Prepare for Midterm DODON'T  Make cheat sheets for the test  Converting to & from decimal  Add post-its to important pages  Review what parts of C++ do  Assume notes replace studying  Memorize  Drink case of 40s before test  Use post-its as clothing

For Next Lecture  Read about arrays in Section 10.5  How can we pass arrays as parameters?  Can values be changed in the array no matter what?  Why couldn't they be consistent about params?  Midterm on Tuesday  Test will be open-book, open-note, but closed activity  Programming Assignment #2 now on Angel  This is a larger assignment; start it now!