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Arrays

Learn about arrays, how they help organize large amounts of information, and how to use them effectively. Explore array declaration, initialization, input/output, and array processing. Understand one-dimensional and two-dimensional arrays.

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Arrays

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  1. Arrays

  2. Arrays Arrays are objects that help us organize large amounts of information

  3. The entire array has a single name Each value has a numeric index scores 79 87 94 82 67 98 87 81 74 91 Arrays • An array is an ordered list of values 0 1 2 3 4 5 6 7 8 9 An array of size N is indexed from zero to N-1 This array holds 10 values that are indexed from 0 to 9

  4. 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

  5. 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]);

  6. 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.

  7. 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

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

  9. 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)

  10. problem 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;

  11. 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'};

  12. 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

  13. 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] ); }

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

  15. 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]);

  16. 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];

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

  18. Example Find the output of the following program: #include<stdio.h> 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; }

  19. 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]); }

  20. 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--; }

  21. 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);

  22. 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.

  23. Example • Write a program that reads in an array of 10 integers (range 0 - 50, strict) and then draws a bar chart of the values: 10 ********** 5 ***** 15 *************** ….

  24. one dimension two dimensions 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

  25. Declaration • int A[3][3] • double B[3][3] • float C[6][6]

  26. 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;

  27. 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]);

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

  29. 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

  30. The End

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