ARRAYS

1. Abstract Data Type in C , Arrays in C ARRAYS

2. The Abstract Data Type • Array is a “consecutive set of memory locations”. • Here we consider array as ADT. • Here more concerned with the operation that can be performed on an array. • Most language provide only two std. operations for arrays- • Retrieves a value • Store a value

3. Definition Abstract Data Type array Return the value associated with the index if the index is valid , or an error if the index is invalid. Store accepts an array , in index , an item ,and return the original array augmented with the new <index ,value > pair.

4. Arrays in C • A one-dimensional array is declared implicitly by appending brackets to the name of a variable • E.g.:- int list[5], *plist[5]; • It declares two arrays each containing 5 elements • 1st defines array is 5 integers,2nd defines 5 pointers to integers. • In c, array index starts at 0,it may has list[0],list[1],list[2],list[3] and list[4](abbrevated list[0:4]

5. Cont…. • The address of the first element list[0],is called the base address. • The size of int is denoted by sizeof(int) so the memory address of list[i] is α+i*sizeof(int). Alpha(α) is base address • When we write list[i] in c program , c interprets it as a pointer to an integer whose address is α+i*sizeof(int).

6. Cont.. Observe the diffrence between declaration • int *list1; • int list2[5]; • list1 and list2 both pointers to an int, but in the second case 5 memory locations are reserved. • List2 is a pointer to list2[0] and list2 +i is a pointer to list2[i]. • In C we do not multiply offset i with the size of the type to get to the appropriate element of array. • So in the case of array list[2] it is always the case that (list2 +i) equals &list2[i].So *(list2 +i) equals list2[i]

7. Program… #define MAX_SIZE 100 float sum(float [], int); float input[MAX_SIZE], answer; Void main (void) { inti; for(i=0;i<MAX_SIZE;i++) input[i]=i; answer=sum(input,MAX_SIZE); printf(“The sum is :%f\n”,answer); } float sum(float list[],int n) { inti; float tempsum=0; for(i=0;i<n;i++) tempsum+=list[i]; return tempsum; }

8. Description of program • When sum() is invoked input=&input[0] is copied into a temporary location and associated with the formal parameter list. • When list[i] occurs on the right hand side of the equal sign, a de-reference takes place and the value pointed at by (list+i) is returned. • If the list[i] occurs on the left hand side of the equal sign, then the value produced on the right hand side is stored in the location (list+i). • Thus in C array parameters have their values altered,despite the fact that the parameter passing is done by call-by-value.

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