EENG 212 Lab 2. Recursive Functions

Transcription

1 EENG 212 Lab 2 Outline - Recursive Functions - Arrays Recursive Functions As it was said before modules in C are called functions. One of the types of functions is a recursive function. A recursive function is a function that calls itself for further simplified processing. As the function calls itself the task is divided into more manageable subtasks. The recursive function calls continuously till a known base-case is found. A typical recursive function has a recursive formula and a base case. Example: Consider the factorial problem: n!=n*(n-1)! (recursive formula) 1!=1*(0!) (base-case) The recursive function that can be written for calculating a recursive function is as follow: int factorial (int a) if ( (a==0) (a==1) ) return 1; else return ( a * factorial(a-1) ); Iteration and recursive functions, both are doing the same. In a recursive problem there are two important points which needs to be considered: 1. Recursive formula 2. Base-Case 1

2 Arrays Arrays are structures of the related data items. They are consecutive memory locations with same name and type. Arrays are declared by stating the following: The type of the values to be stored A variable identifier (The name of the array) The number of elements in the array Example: The following statement declares an array to store 100 int values int b[100]; Note: The size of the array has to be specified when declaring an array; otherwise, an error will be generated. Note: The first element of an array is at position 0. Assigning values to Arrays The following program shows how to read the elements of an array from the keyboard, using a scanf statement and a for loop to cycle through each element in turn. #include <stdio.h> main() int count; float b[4]; for( count = 0; count < =3; count++ ) scanf( %d,&b[count]); Strings as Arrays Strings in C are character arrays with a terminating character \0. For character arrays we have two ways of specifying initial values: E.g. char vowels[]= E, E, N, G, 2, 1, 2, \0 ; or char vowels[]= EENG212 ; In both cases, the character array (string) vowels, has a size of 8 with contents EENG212 terminated with an invisible end marker (\0) for a string. A string can also be read in the following way: char name[40]; scanf ( %s,name); where %s stands for string. Arrays as Parameters to Function As we said every parameter of a C function must be declared within the function. However, the size of a one-dimensional array parameter is only specified in the main program. Example: Consider the following function to calculate the average of the elements of an array. 2

3 float avg(float a[], int size) int i; float sum=0; for(i=0;i<size;i++) sum+=a[i]; return(sum/size); A main program to call this function could be: #include<stdio.h> #define SIZE 10 float avg(float a[], int size); int main() float a[size],average; for (int i=0;i<size;i++) scanf( %d,&a[i]); average= avg(a,size ); //call by reference printf( The average of the %d numbers is %f,size,average); return 0; Sorting Arrays Sorting of an array is ordering the elements of an array in ascending (increasing from minimum to maximum) or descending (decreasing from maximum to minimum) order. Bubble Sort (ascending form): In this type of sorting, the technique makes several passes through the array on each pass successive pair of elements is compared. If a pair is in increasing order (or equal) the pair is unchanged, otherwise the value of the pair are swapped. The following piece of code is a typical coding of the bubble sort: for (int pass=1;pass<=size-1;pass++) for (int i=0;i<=size-2;i++) if (A[i]>=A[i+1]) hold=a[i]; A[i]=A[i+1]; A[i+1]=hold; Searching Arrays There are two typical kinds of search algorithms: Linear Search: it is very simple and useful for small and unsorted arrays. Here we need a key value. Binary Search: It is fast and with 2 n elements n steps are required. 3

4 Linear Search: The process of finding a key element in an array is called searching. The linear search compares each array element with the search key one by one from the beginning of the array to the end of the array. The following piece of code is a typical coding of the linear search (for an array of integer numbers): int LinearSearch(int x[], int SearchKey) int i; for (i=0;i<=size-1;i++) if (x[i]==searchkey) return i; return -1; Binary Search: Binary search is a faster algorithm than the ordinary linear search. Binary search can only be used for sorted arrays. The following piece of code is a typical coding of the binary search (for an array of integer numbers): int BinarySearch(int x[], int SearchKey) int middle,low,high; low=0; high=size-1; while (low<=high) middle=(low+high)/2; if (SearchKey==x[middle]) return middle; else if (SearchKey<x[middle]) high=middle-1; else low=middle+1; return -1; Multidimensional Arrays An array whose elements are themselves arrays is called a multi-dimensional array i.e. an array whose elements are one-dimensional arrays in a two-dimensional array. Example: This program segment reads in a 2-dimensional character array char name[4][25]; for(int i=0;i<=3;i++) scanf( %s,name[i]); 4

5 Lab Work 1. Write a C program to produce Fibonacci series (use recursive function). The following series of numbers is known as Fibonacci series: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, (HINT: The recursive formula is: fib(n) = fib (n-1) + fib (n-2) and the base cases are: fib(1) = 1 fib(0) = 0 ). 2. Write a C program to read in 4 students names, their numbers and their GPAs. The program should then print out the data for each student. (HINT: Use a 2 dimensional character array for the names and 2 one-dimensional arrays for the numbers and the GPAs). 3. Write a C program to read the following arrays: a=10,2,13,4,-5,-6,7,8,19, 0 b=11,3,6,18,-10 In the programme use the SortArry and MinMaxArry functions to print the sorted array, the minimum and maximum of each array. H.W. 2.a (Due after one week) Write a program that uses a recursive function IntegerPower(base, exponent) that returns the value of base exponent. H.W. 2.b (Due after one week) Write a C programme that read a word and print it in the reverse order. For example if the user enters EENG212, the programme should print 212GNEE. Also inside the programme use the function VowCnt to count the number of vowels letters in that word. NOTES: Write the LAB No. on the s subject Send the to the following address: shahab.jafari@cc.emu.edu.tr (You will receive a delivery report from me, if you have not it means that I have not got your assignment!). Late submission will not be accepted! Gh. Anbarjafari (Shahab)