Arrays

Arrays are objects that help us organize large amounts of information

Arrays An array is an ordered list of values An array of size N is indexed from zero to N-1 scores The entire array has a single name Each value has a numeric index This array holds 10 values that are indexed from 0 to 9

Arrays A particular value in an array is referenced using the array name followed by the index in brackets For example, the expression scores[2] refers to the value 94 (the 3rd value in the array) That expression represents a place to store a single integer and can be used wherever an integer variable can be used

Arrays For example, an array element can be assigned a value, printed, or used in a calculation: scores[2] = 89; scores[first] = scores[first] + 2; mean = (scores[0] + scores[1])/2; printf ("Top = %d”, scores[5]);

Arrays The values held in an array are called array elements The element type can be a primitive type or a structure. Therefore, we can create an array of integers, or an array of characters, or an array of String objects, etc.

Declaring Arrays The scores array could be declared as follows: int scores[10] ; The type of the variable scores is an array of integers The variable scores is set to a new blank array that can hold 10 integers

Declaring Arrays Some examples of array declarations: double prices[500] ; int factor[12], age[6]; char codes[30] ;

Bounds Checking Once an array is created, it has a fixed size That is, the index value must be in bounds (0 to N-1)

Bounds Checking For example, if the array codes can hold 100 values, it can be indexed using only the numbers 0 to 99 If count has the value 100, then the following reference will cause a problem: for (int index=0; index <= 100; index++) codes[index] = index*50 + epsilon; problem

Initializer Lists An initializer list can be used to instantiate and initialize an array in one step Examples: int units[] = {147, 323, 89, 933, 540, 269, 97, 114, 298, 476}; char letterGrades[] = {'A', 'B', 'C', 'D', ’F'};

Initializer Lists Note that when an initializer list is used: no size value is specified The size of the array is determined by the number of items in the initializer list An initializer list can only be used only in the array declaration

Array Input/ Output We typically use for loops for any kind of array processing. To input an array, one by one: for (i=0; i<10 ; i++ ) { printf(“ Enter element %d : “, i ); scanf ( “ %d “, &scores[i] ); }

Array Output To display an array, one element per line: for (i=0; i<10 ; i++ ) { printf(“ scores [%d] : %d\n“, i, scores[i] ); }

Example double X[ ]= {16.0, 12.0, 6.0, 8.0, 2.5, 12.0, 14.0, -54.5} int i=5; printf(“%f”, x[4]); printf(“%f”, x[i]+1); printf(“%f”, x[i+1]); printf(“%f”, x[2*i]);

Example double X[ ]= {16.0, 12.0, 6.0, 8.0, 2.5, 12.0, 14.0, -54.5} int i=5; printf(“%f”, x[2*i-3]); printf(“%f”, x[(int) x[4]]); printf(“%f”, x[i++]); printf(“%f”, x[--i]); x[i]= x[i+1];

Example int Squre[10], I; for (I=0; I<10; I++) Squre[I]=I * 2 ;

Example Find the output of the following program: #include int main() { int q[]= {3, 1, 4, 2}; float n[]={3.0, 1.0, 2.0, 7.0}, s=0; for(int j=0; j<3; j++) s+= n[q[j]-1]; printf(“%f”, s); return 0; }

Find the output for(j=0; j<7;j++) A[j]=7-j; for(p=6; p>3; p--){ K=p-1; While(k>2){ T = A[p-k]; A[p-k] = A[7-p+k] A[7-p+k]= T } printf(“%d”, A[p]); }

Trace the program int X[7] = {12, 25, 4, 9, 0, -1, 12} for (int j=5; j>=0; ) { printf(“%d”, X[j+1]); j--; }

Find the output int A[7], sum =0; for(int j=0; j<7;j++) A[j]=7-j*3; for(int p=6; p>3; p--){ printf(“%d”, A[p]); sum=sum + A[p]; if(A[p]<2) printf(“%d”, p); } double Avg = sum / 7; printf(“%f”, Avg);

Example Write a program that reads in an array of 10 elements, gets their average, and then display the deviation of each element from that average.

Example Write a program that reads in an array of 10 integers (range , strict) and then draws a bar chart of the values: 10********** 5***** 15*************** ….

Two-Dimensional Arrays A one-dimensional array stores a list of elements A two-dimensional array can be thought of as a table of elements, with rows and columns one dimension two dimensions

Declaration int A[3][3] double B[3][3] float C[6][6]

Using To use 2-dimensional array we use 2 for-loop as for(i=0; i<3;i++) for(j=0; j<3; j++) A[i][j]=i*j;

Trace the program int A [3][3]= {{1, 7, 12}, {-2, 0, 4}, {45, 5, 4}} for(int i=1; i<3; i++) for(int j = 1; j<3; j=j+i) printf(“%d”, A[i][j]);

Program Write a program that read two matrices of size 5x5. and add two matrices to another one which will be displayed.

Example Write a C program to find the average of vector elements in 2-D matrix. For example, you are given matrix A[5][5] and index 3, so you will print the average of elements in raw 3

The End