CHAPTER 6 ARRAYS IN C 1 st semester King Saud University College of Applied studies and Community Service Csc 1101 F. Alakeel

Introduction to Arrays  Arrays  Structures of related data items  same types of data and same name  Represented as a group of consecutive memory locations  Static entity – same size throughout program F. Alakeel

Defining Arrays  When defining arrays, specify  Name  Type of array  Number of elements arrayType arrayName[ numberOfElements ];  Examples: int c[ 10 ]; float myArray[ 3284 ];  Defining multiple arrays of same type  Format similar to regular variables  Example: int b[ 100 ], x[ 27 ]; F. Alakeel

- Examples- Defining Arrays  int A[10] An array of ten integers A[0], A[1], …, A[9]  double B[20] An array of twenty long floating point numbers B[0], B[1], …, B[19]  Array indexes always start at zero in C

Example- Defining Arrays  Examples  Define an array temperature of float with size 5 : float temperature [5]; F. Alakeel

Initializing Arrays  Initializers int n[ 5 ] = { 1, 2, 3, 4, 5 };  If not enough initializers, rightmost elements become 0 int n[ 5 ] = { 0 } All elements 0  If too many initializers, a syntax error occurs  C arrays have no bounds checking  If size omitted, initializers determine it int n[ ] = { 1, 2, 3, 4, 5 };  5 initializers, therefore 5 element array F. Alakeel

Initializing Arrays  int A[5] = {2, 4, 8, 16, 32};  int B[20] = {2, 4, 8, 16, 32}; Unspecified elements are guaranteed to be zero  int C[4] = {2, 4, 8, 16, 32}; Error — compiler detects too many initial values  int D[5] = {2*n, 4*n, 8*n, 16*n, 32*n}; Automatically only; array initialized to expressions

Initializing Arrays - Example  double temperature [5]= {12.3,7.5,65,72.1,87.5};  Or - double temperature[]= {12.3,7.5,65,72.1,87.5}; temperature [0] temperature [1] temperature [2] temperature [3] temperature [4] F. Alakeel

double temperature [5]; Elements temperature [0] temperature [1] temperature [2] temperature [3] temperature [4] F. Alakeel

double temperature [5]; Subscript or Index temperature [0] temperature [1] temperature [2] temperature [3] temperature [4] F. Alakeel

1.Use assignment statements. See the next slide. 2.Initialize arrays in the variable declaration statement  ex:double temperature [5]= {12.3,7.5,65,72.1,87.5}; 3.Read input values into the array from the keyboard or from a file Three ways to get values into array elements F. Alakeel

declaration: int score [6]; score: index: (Subscript) score[0]=49; score[1]=75; score[2] = 65; score[3] = 90; score[4]=77; score[5]=70; F. Alakeel

Array Element  May be used wherever a variable of the same type may be used In an expression (including arguments) On left side of assignment  Examples:– A[3] = x + y; x = y – A[3]; z = sin(A[i]) + cos(B[j]);

Accessing Array Elements temperature [4] = 12.7; or N = 4; temperature [N] = 12.7; F. Alakeel

Accessing Array Elements  To refer to an element, specify  Array name  Position number  Format: arrayname [ position number ]  First element at position 0  n element array named c: c[ 0 ], c[ 1 ]...c[ n – 1 ] F. Alakeel

Accessing Array Elements  Array elements are like normal variables c[ 0 ] = 3; printf( "%d", c[ 0 ] );  Perform operations in 4th subscript. (x=3) c[ ] == c[ 3 ] == c[ x ] F. Alakeel

Assigning Values  We cannot use assignment statements with entire arrays.  Instead, we must assign values to individual elements  We can use them as values in assignment statements: score[0] = 30; grade[3] = ‘A’; price[2] = 10.39; F. Alakeel

Using Array Elements  All of the following are valid: score[0] = 4; score[0] += 7; score[1] = score[0] -2; score[2] = score[1] + 5 * score[0]; score[j] = score[j + 1];  Note: index can be any integral expression. F. Alakeel

Example  Array elements are commonly used in loops  E.g., for(i=0; i < max; i++) A[i] = i*i; for(sum = 0, j=0; j < max; j++) sum += B[j]; F. Alakeel

Note  The index of array starts at 0.  To access the seventh element in array C, we type: C[6] =10; Note that we used 6 instead of 7. F. Alakeel

Manipulating Arrays  To access all elements of an array a for loop is used.  For loop will start from index 0 to the last element in the array which has an index of array size-1 F. Alakeel

Note  When looping through an array, the array index should  never go below 0 and  always be less than the total number of elements in the array (size – 1).  Make sure the loop-terminating condition prevents accessing elements outside this range. F. Alakeel

Manipulating Arrays  For loops are used to:  Initializing array elements  Reading elements  Printing elements  Performing operations Sum elements Find largest/ smallest element Search for an element Sort elements F. Alakeel

Initializing Array Elements –Using For loop  Example: to initialize array a of size 10 with zeros, the for loop should go from 0 until 9, the syntax is: int size=10; int a[size],index; for(index =0; index<=size-1; index++) a[index] = 0; F. Alakeel

Reading Elements – without For Loop Examples: float temperature [5]; Reading: scanf(“%f”, &temperature [0]); scanf(“%f”, &temperature [1]); scanf(“%f”, &temperature [2]); scanf(“%f”, &temperature [3]); scanf(“%f”, &temperature [4]); F. Alakeel

Reading Elements – using For Loop Ex1: int i; for(i=0; i<5; i++) { scanf(“%f”,&temperature[i]); } Ex2: for(index =0; index<=size-1; index++) { printf(“Enter value>”); scanf(“%d”,&a[index]); } F. Alakeel

Printing Elements – without For Loop Examples: float temperature [5]; Printing: printf(“%f”,temperature [0]); printf(“%f”,temperature [1]); printf(“%f”,temperature [2]); printf(“%f”,temperature [3]); printf(“%f”,temperature [4]); F. Alakeel

Printing Elements – Using For Loop Ex1: int i; for(i=0; i<5; i++) { printf(“%f”,temperature[i]); } Ex2: for(index =0; index<=size-1; index++) { printf(“%d”,a[index]); } F. Alakeel

Sum the elements int sum=0; for(index =0; index<=size-1; index++) { sum = sum + a[index]; } F. Alakeel

for loop initializes each array element separately for loop outputs all array elements Element Value F. Alakeel

initializer list initializes all array elements simultaneously Element Value F. Alakeel

Outline fig06_05.c (1 of 2 ) #define directive tells compiler to replace all instances of the word SIZE with 10 SIZE is replaced with 10 by the compiler, so array s has 10 elements for loop initializes each array element separately F. Alakeel

Outline fig06_05.c (2 of 2 ) F. Alakeel

Outline fig06_06.c initializer list initializes all array elements simultaneously for loop adds each element of the array to variable total F. Alakeel

Array Practice 1. Declare an array to hold the tax for up to 10 different sales. 2. Declare an array to hold the final letter grades for a class with up to 40 students 3. Declare an array of integers which holds the final average for those 40 students and initialize its values to 0 4. Declare an array of characters called letter_ary with initial values ‘a’, ‘d’, ‘y’, and ‘w’. What is the value of letter_ary[1]? F. Alakeel

More Array Practice  Write a loop to initialize all 50 elements of array salary_ary to 100.  Write C code to read values from the keyboard to fill the array scores. Input should stop when a negative number is entered. The maximum size of the array is in a constant ARR_SIZE.  Write C code to add up the first num_elements values in the array my_vals and store the sum in the variable my_sum. F. Alakeel

ARRAY OF CHARACTERS F. Alakeel

Array of Characters  Character arrays  String “first” is really a static array of characters  Character arrays can be initialized using string literals char string1[] = "first"; Null character '\0' terminates strings string1 actually has 6 elements It is equivalent to char string1[] = { 'f', 'i', 'r', 's', 't', '\0' };  Can access individual characters string1[ 3 ] is character ‘s’  Array name is address of array, so & not needed for scanf scanf( "%s", string2 ); Reads characters until whitespace encountered Be careful not to write past end of array, as it is possible to do so F. Alakeel

Common Programming Error 6.7  Not providing scanf with a character array large enough to store a string typed at the keyboard can result in destruction of data in a program and other runtime errors. This can also make a system susceptible to worm and virus attacks. F. Alakeel

Outline fig06_10.c (1 of 2 ) string2 array is defined with one element for each character, so 15 elements including null character /0 for loop prints characters of string1 array with spaces in between F. Alakeel

Outline fig06_10.c (2 of 2 ) F. Alakeel