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Arrays
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Introduction Chapter to Arrays
A collection of data of same type Used for lists of like items temperatures, names, etc. Avoids declaring multiple simple variables Can manipulate `list' as one entity
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Introduction to Arrays
Used when we need to keep lots of values in memory
Sorting Determining the number of scores above/below the mean Printing values in the reverse order of reading
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Declaring Arrays
Static entity same size throughout program Declaring the array allocates memory
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Declaring Arrays
General Format for declaring arrays Examples int scores[300]; float hi[3284]; char alphabet[26];
<data type> <variable> [<size>];
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Declaring Arrays
Individual parts called many things: Indexed or subscripted variables Elements of the array Value in brackets called index or subscript Numbered from 0 to (size 1)
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Accessing Array Elements
To refer to an element of an array, specify Array name and position number Format: arrayname[position number ] Example rainfall[0] refers to the first element of array rainfall
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Accessing Array Elements
Example Printf("%d", score[3]); Note two uses of brackets: In declaration, specifies SIZE of array Anywhere else, specifies a subscript/index
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Accessing Array Elements
Example
Given the declaration int rainfall [28], we reference elements of rainfall by
rainfall [0], rainfall [1], ... rainfall [27]
subscript/index
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Accessing Array Elements
Size, subscript need not be literal int score[MAX_SCORES]; score[n+1] = 99; If n is 2, identical to: score[3]
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Array Usage
Powerful storage mechanism Can issue command like: "Do this to ith indexed variable" where i is computed by program "Display all elements of array score"
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Array Usage
Can issue command like: "Fill elements of array score from user input" "Find highest value in array score" "Find lowest value in array score"
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forloops with Arrays
Natural counting loop Naturally works well 'counting thru' elements of an array
Example: (index for = 0; index<5; index++) { printf("%d", score[index]); }
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Major Array Pitfall
Array indexes always start with zero! C will 'let' you go beyond range Unpredictable results Compiler will not detect these errors!
Up to programmer to 'stay in range'
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Defined Constant as Array Size
Use defined/named constant for array size Example:
const int NUMBER_OF_STUDENTS =5; int score[NUMBER_OF_STUDENTS];
Improves readability Improves versatility Improves maintainability
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Uses of Defined Constant
Use everywhere size of array is needed In forloop for traversal:
for (index = 0; index < NUMBER_OF_STUDENTS; index++) { // Manipulate array }
In calculations involving size:
lastIndex = (NUMBER_OF_STUDENTS 1);
When passing array to functions
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Initializing Arrays
Arrays can be initialized at declaration. int data[3] = {2, 12, 1}; Equivalent to the following:
int data[3]; data[0] = 2; data[1] = 12; data[2] = 1;
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AutoInitializing Arrays
If fewer values than size supplied: Fills from beginning Fills 'rest' with zero of array base type Example:
int b[5] = {5, 12, 11}; b[0] = 5 b[1] = 12 b[2] = 11 b[3] = 0 b[4] = 0
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AutoInitializing Arrays
If arraysize is left out Declares array with size required ...