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lecture9

# lecture9 - Wednesday November 3 rd Arrays,Part#2 Array...

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Wednesday, November 3 rd Arrays, Part #2 Searching Through Arrays Double Dimensional Arrays ADD HOW TO PASS 2-D ARRAYS TO FUNCTIONS!!!!

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Array Challenge int main(void) { const int NUM_STUDS = 3; int grades[NUM_STUDS] = {0}; int j=0; while(j++<NUM_STUDS) { cout << “Enter grade “ << j << “: “; cin >> grades[j]; } int avg; for (j=0;j<NUM_STUDS;j++) avg += grades[j]; avg /= NUM_STUDS; cout << “The average is: “ << avg; } Find all  of the problems  in this program. grades          0 0 0          j           0 < 3  1 Enter grade 1: 90 90 0 1 2 1 < 3  2 Enter grade 2: 80 80 2 < 3  3 Enter grade 3: 30 30 BOOM!
Not Entirely Full Arrays Sometimes we don’t  know how many items  we want to store in our  array ahead of time. int main() { const int MAX_CS_PROFS = 30; // MAX! int actual_profs = 0; string names[ MAX_CS_PROFS ]; while ( actual_profs < MAX_CS_PROFS ) { cout << “Enter name (blank=done): “; cin >> names[ actual_profs ]; if (names[ actual_profs ] == “”) break; ++ actual_profs ; // we just added one } // print out as many names were entered for (int j=0;j< actual_profs ;j++) cout << names[j] << “\n”; In this case, we must  make our array big  enough to hold the  maximum expected  number of items.

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You then use another  variable to indicate how  many items are  actually   in the array. int main() { const int MAX_CS_PROFS = 30; // MAX! int actual_profs = 0; string names[ MAX_CS_PROFS ]; while ( actual_profs < MAX_CS_PROFS ) { cout << “Enter name (blank=done): “; cin >> names[ actual_profs ]; if (names[ actual_profs ] == “”) break; ++ actual_profs ; // we just added one } // print out as many names were entered for (int j=0;j< actual_profs ;j++) cout << names[j] << “\n”; This variable will be less  than or equal to the  maximum number of  items. Not Entirely Full Arrays
Global and Static Arrays Static  and  global  arrays behave  exactly like regular  static  and  global   variables :  1. If they’re not explicitly initialized by  the user, all elements are set to 0. 2. Statics are initialized only once, the  first time the function is called. 3. Static or global arrays maintain their  value between function calls. 4. Static arrays are only visible to the  function where they’re defined.  #include <iostream> int ages[10]; // global array void print_ages(void) { for (int i=0;i<10;i++) cout << ages[i] << endl; } void record_rainfall(int amt) { static int rain[52]; // static // array! static int week = 0; rain[week++] = amt; } main()

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Passing Arrays to Functions int sum(int array[], int elems) { int i, total = 0; for (i=0;i<elems;i++) total += array[i]; return(total); } void main(void) { int money[5] = {40,30, 10, 10, 10}; int result; result = sum(money,5); cout << result << endl; } The general form is:     type varname[ ]    e.g.      int arrayname[ ]   This is how you define a    formal array parameter.
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