# An Array A sequence of elements of a particular type Each element in the array has an index which gives its position in the sequence An array is declared.

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An Array A sequence of elements of a particular type Each element in the array has an index which gives its position in the sequence An array is declared int a[10] which declares an array of 10 integers whose indices go from 0-9

 The length of the array is set when it is created. It cannot change.  Individual array elements are accessed via an index.  Array index numbering starts at 0. Length of Arrays

Arrays An array: an object that can hold a fixed number of values of the same type. Array to the right contains 4 int values. 5 7 4 -2 a0 A declaration has the basic form [arraylength] ; int x[10] ; 01230123 Elements of the array are numbered 0, 1, 2, …, x.length–1; length is a variable, not a function, so don’t put () after it. The type of the array to the right is int Here is a variable that contains the name of the array. x a0 int[] Make everything as simple as possible, but no simpler. Einstein

Arrays -4 0 6 -8 a0 01230123 Assign 2*x[0], i.e. -8, to x[3] Assign 6 to x[2] int k= 3; x[k]= 2* x[0]; x[k-1]= 6; x[2]= 5; x[0]= -4; -4 0 5 0 a0 01230123 Assign 5 to array element 2 and -4 to array element 0 x[2] is a reference to element number 2 of array x

Array initializers Instead of int c[5]; c[0]= 5; c[1]= 4; c[2]= 7; c[3]= 6; c[4]= 5; Use an array initializer: int c[5]= {5, 4, 7, 6, 5}; 5476554765 a0 array initializer: gives the values to be in the array initially. The values must all have the same type, in this case, int. The length of the array is the number of values in the list Computer science has its field called computational complexity; mine is called computational simplicity. Gries

Processing Array Elements Access individual elements of an array using: –the name (handle) of the array –a number (index or subscript) that tells which of the element of the array What value is stored in count[2] ? count[0] [1] [2] [3] 5 -7 9 27

Processing Array Elements Often a for( ) loop is used to process each of the elements of the array in turn. for (int i = 0; i < NUM_STUDENTS; i++) {); } The loop control variable, i, is used as the index to access array components

Some exercises Write a program which finds the maximum of an array Write a program which finds the average of a list of integers

Largest of 10 Integers #Include main() { int i, a,max; printf(“enter number \n”); scanf(“%d”,&a); max = a; for (i=1;I < 10; i++) { printf(“enter number \n”); scanf(“%d”,&a); If (a > max) max = a; }; printf(“largest is %d”,max); }

Largest of 10 Integers #Include main() { int i, max; int a[10]; printf(“enter number \n”); scanf(“%d”,&a[0]); max = a[0]; for (i=1;I < 10; i++) { printf(“enter number \n”); scanf(“%d”,&a[i]); If (a[i] > max) max = a[i]; }; printf(“largest is %d”,max); }

Largest of 10 Integers #Include main() { int i, max; int a[10]= {7,3,4,28,4,56,12,3,44,7} max = a[0]; for (i=1;I < 10; i++) If (a[i] > max) max = a[i]; }; printf(“largest is %d”,max); }

 Arrays with multiple dimensions can also be created.  They are created and initialized in the same way as single dimensioned arrays. Multi-dimensional Arrays type arrayName[rowlength] [collength]; declaration syntax: intgrades[20][5]; for(int i = 0; i< 20; i++) for(int j = 0; j<5; j++) grades[i][j] = 100;

Exercises Write Programs to 1: given an array of 20 Integers print out all those > 15 and print out their positions. 2: Given an array of 20 integers, delete the 5 th element so that: Before 17-15-14-23-22-19-etc After 17-15-14-23-19-etc

Exercise Write a program which takes an array and reverses it.

We could use scanf and a for loop #include main() { int a[10] int i for ( i = 0;i < 10 ; i++) { printf(“enter a number”); scanf(“%d”,&a[i]); } for ( i = 0;i < 10 ; i++) printf(“the %d th number in the arrray is %d \n”,i,a[i]); for ( i = 9;i >= 0 ; i--) printf(“the %d th number in the arrray is %d \n”,i,a[i]); }

Exercise Write a program to enter 10 numbers into an array and to print out the maximum element of the array.

We could use scanf and a for loop #include main() { int a[10] int I; Int max; Printf(“enter first number”); scanf(“%d”,&a[0]); max = a[0]; for ( i = 1;i < 10 ; i++) { printf(“enter a number”); scanf(“%d”,&a[i]); If (a[i] > max) max = a[i]; } printf(“the max number in the arrray is %d \n”,max); }

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