1. Introduction to C Programming
ET2560 Introduction to C Programming
Introduction to C Programming
Unit 8 Arrays and Strings
Unit 1 Presentations

2. Unit 7 Review
Unit 8: Review of Past Material

3. Functions - Review Function Header Function Body Return Type
Identifier - name of function
Parameter List
Data type and Identifier for each parameter
Comma-separated list, enclosed in parentheses
Function Body
Compound Statement in braces
Must contain a return statement unless return type is void

4. Variable Scope Global variable Local variable Block scope
Declared at top of a file
Accessible throughout the compilation
Local variable
Declared inside a function at top of function body
Known only within the function
Block scope
Declared inside a nested compound statement (block of code)
Known only within the block
Two or more variables with same name - the one at the smaller scope hides the one(s) at larger scope(s)

5. Pointers
Pointer has a data type corresponding to the variable pointed to
Pointers are declared using the "*" asterisk character
The address of a variable is obtained using the "&" character
To use a pointer to access memory, precede it with "*"
Used to create output parameters for functions
Each output parameter is declared as a pointer
The function call must use the address of a variable as the argument
Inside the function, the external variable is accessed by pointer

6. Arrays
Unit 8: Arrays and Strings

7. Data Structures Group of related data items
Stored in one contiguous area of memory
Can be accessed and manipulated as a group or unit
Record (C language "struct")
Combination of data items of various data types
Each data item called a "field" in the record
Array (C language "array")
Multiple data items of matching data type
Each data item called an "element" in the array

8. Arrays - Declaration
Data type, variable identifier, size in square brackets
Size must be a constant expression, not a run-time expression
Size must be a positive integer
int numbers [ 5 ];
The example above declares an array variable of 5 elements
The elements are numbered starting from 0:
numbers[0], numbers[1], numbers[2],
numbers[3], numbers[4]
Notice that the last element is "4", not "5" !

9. Arrays - Access to Array Elements
The element is identified by its index (numerical position)
Name of array (identifier) followed by subscript
Subscript is index in square brackets
Index value must be integer expression
Examples using the numbers array:
value = numbers[10];
value = numbers[i+2];
numbers[4] = value + 3;
numbers[0] =

10. Arrays - Caution! Array element numbering (index) starts at 0, not 1
The elements are numbered [0], [1], [2], … [n-1]
int numbers[5];
numbers[0], numbers[1], numbers[2],
numbers[3], numbers[4]
Common Programming Error:
Accessing past end of array - logic error
numbers[5]
C Language does not check for this error

11. Array Initializers
Follow array declaration with a list of expressions in braces
int numbers[5] = {3, 12, -42, 0, 6};
If a size is specified, and list is too short, zeros are used at end
If a size is specified, and list is too long, this is an error
If a size is not specified (empty square brackets)
The compiler counts the number of initializers
The count is used as the size
int numbers[] = {3, 12, -42, 0, 6};

12. Array Usage - Parallel Arrays
Parallel Arrays - Arrays of related data items
Example: A list of 100 rectangles, dimensions length and width
Use two arrays of doubles, each size 100
double length[100], width[100];
length[i] = 40;
width[i] = 25;

13. Array Usage - Use with Functions
Arrays and Functions
An element can be passed as an argument to a function
area = calcArea(length[3], width[3]);
An entire array can be passed as an argument to a function
Size not passed automatically, must be an explicit separate parameter
f(numbers, 5);
An array cannot be returned from a function

14. Multi-Dimension Arrays
Arrays can have one to six dimensions
A two-dimensional array is like a grid
The first dimension is the row, second is the column
Specify each size in separate square brackets
double grid[50][25];
When accessing, provide separate subscripts
grid[r][c] = 42.5;

15. Multi-Dimension Arrays
When initializing, initialize one row at a time
Initializer is "list of lists"
Use braces for the entire list
Use braces for list of initializers for each row
double xy[4][3] = { {0, 12.2, 14.7}, {2.5, 8.3, -6}, {2.0}, /* "Short" list filled with zeros */ {1E6, 3.2E-1, 47.9} };

16. Searching and Sorting
Unit 8: Arrays and Strings

17. Searching Often-used algorithm
Goal: Find a value, discover it's index
May have result of "not found"
Array is list of values, look through the list
Is the list unsorted (random order)? Linear Search pp
Look through each element from beginning
Finds the first occurrence
Is the list sorted (sequential order) ? Binary Search
Divide list in half
Finds one occurrence, not necessarily the first
More efficient than linear search (over the long run)

18. Sorting Common, often-used algorithms
Many sort algorithms have been developed
Simple, but less efficient
Complex, faster performance
Example: Selection Sort pp
Find smallest element (first occurrence) in list [0] … [n-1]
Swap smallest element with first element
Now, use Selection Sort on remaining list [1] … [n-1]
Continue until the "remaining unsorted list" has 1 element

19. String Variables: Arrays of Characters
Unit 8: Arrays and Strings

20. Strings Important, commonly-used data type
Group of characters treated as a unit
Examples of common uses
Names of people, places, devices, etc
Instructions to user
Error messages
Web addresses and URLs

21. C Language Strings C does not actually have a string data type
A C string uses a character array
The string begins with the 0th element, might not fill array
To indicate end of string, a sentinel 0-value character is used
The sentinel must always be present
char s1[10] = "George";
The format specifier for printf and scanf is "%s" G e o r g \0