1. Fucntions in C++ Malik Jahan Khan
Functions in C++
Malik Jahan Khan
Malik Jahan Khan

2. Fucntions in C++
Functions
A function groups a number of program statements into a unit and gives it a name
Then this unit may be called from other program parts
The most important reason to use functions is to organize the program conceptually
Another reason is to reduce program size by putting repeated parts of program into functions
Dividing the program into functions is the key principle of structured programming
OOP has better principles to organize the program conceptually [We will learn them]
Malik Jahan Khan

3. Functions (Cont.)
Function Prototype void main() { … Function call } Function Declarator Function Body
Function Definition

4. Functions (Cont.) - Example
#include<iostream.h> void starline(); //Prototype void main() { starline(); //Function Call cout<<endl<<“Object Oriented Programming”<<endl; cout<<“OOP is an inspiration from “<<endl<< “real world objects. “<<endl<< “World is made up of objects”<<endl; } void starline() //Function Definition for(int x=1;x<=20;x++) cout<<“*”;
Output:
********************
Object Oriented Programming
OOP is an inspiration from
real world objects.
World is made up of objects

5. Passing Arguments to Functions
Argument is some data passed from the caller to a function which acts as an input to a function
Each argument is specified by its data type
void FunctionName(DataType, DataType); //Prototype
FunctionName(Value, Value); //Call to function
void FunctionName(DataType Var1, DataType Var2) //Function Declarator

6. #include<iostream
#include<iostream.h> void chararcterline(char, int); //Prototype void main() { char a=‘#’; int b=20; characterline(a,b); //Function Call cout<<endl<<“Object Oriented Programming”<<endl; a=‘*’; cout<<“OOP is an inspiration from “<<endl<< “real world objects. “<<endl<< “World is made up of objects”<<endl; a=‘&’; } void characterline(char y,int z) //Function Definition for(int x=1;x<=z;x++) cout<<y;
Example
Output:
####################
Object Oriented Programming
********************
OOP is an inspiration from
real world objects.
World is made up of objects
&&&&&&&&&&&&&&&&&&&&

7. Returning Values from Functions
Arguments are passed from caller to the function
It may also be a scenario when we need the result to be sent back to the caller from the function
It can be accomplished using return statement
The value to be returned must have the same data type as given in prototype and definition of the function
When a fucntion completes its execution, it can return a single value to the calling program
Usually, this returned value is the answer calculated by the fucntion

8. #include<iostream> using namespace std; float lbsToKg(float); //Declaration int main() { float lbs; cout<<“\n Enter your weight in pounds:”; cin>>lbs; cout<<“\n Your weight in Kg is:”<<lbsToKg(lbs); //Call return 0; } float lbsToKg(float pounds) //Definition return *pounds;
Example

9. Multiple Functions We may have multiple functions in a program
Any function can be called from any function as we call our own declared function from main()

10. #include<iostream
#include<iostream.h> int add(int,int); //Declaration int multiply(int,int); //Declaration int main() { int a,b; cout<<“\n Enter first number:”; cin>>a; cout<<“\n Enter 2nd number:”; cin>>b; cout<<“\n Product is:”<<multiply(a,b); //Call return 0; } int multiply(int x, int y) //Definition int i,result=0; for(i=1;i<=y;i++) result=add(result, x); //Call return result; int add(int x, int y) //Definition return x+y;
Example

11. Passing Arrays to a Function
Array name acts as a base address of the whole array
If we only use name of array, then it means we are starting from the first element of the array
We can increment towards next locations just like we increment towards next consecutive houses of friends in a street

12. #include<iostream> using namespace std; int add(int[]); void main() { int i[]={4,6,8,9,10}; int j; cout<<"Sum of array elements is "<<add(i); } int add(int arr[]) int sum=0; for(int x=0;x<5;x++) sum=sum+arr[x]; return sum;
Example
Output
Sum of array elements = 37

13. #include<iostream> using namespace std; int add(int[]); void main() { int i[]={4,6,8,9,10}; int j; cout<<"\n First element before addition ="<<i[0]; cout<<“\n Sum of array elements = "<<add(i); cout<<"\n First element after addition ="<<i[0]; } int add(int ptr[]) int sum=0; for(int x=0;x<5;x++) sum=sum+ptr[x]; ptr[0]=100; return sum;
Example
Output
First element before addition =4
Sum of array elements = 37
First element after addition =100

14. What’s going on! Arrays are passed by reference, not by value
If they would have been passed by value then in the previous example first element of original array would not have been altered
But ordinary variables are passed by value, not by reference

15. #include<iostream
#include<iostream.h> int add(int[],int); void main() { int i[]={4,6,8,9,10}; int j,k=50; cout<<"\n First element before addition ="<<i[0]; cout<<"\n Value of k before addition ="<<k; cout<<"\n Sum of array elements = "<<add(i,k); cout<<"\n First element after addition ="<<i[0]; cout<<"\n Value of k after addition ="<<k; } int add(int ptr[],int k) int sum=0; for(int x=0;x<5;x++) sum=sum+ptr[x]; ptr[0]=100; k++; return sum;
Example
Output
First element before addition =4
Value of k before addition =50
Sum of array elements = 37
First element after addition =100
Value of k after addition =50

16. Homework (ungraded)
Problem: Build a program which takes 8 integers as input array. It also asks for an option:
“i” means Insertion Sort
“s” means Selection Sort
It simulates the corresponding sorting algorithm as selected by user
By simulation, we mean showing all intermediate steps while trying to sort

17. Homework (Cont.)
You MUST write separate function for each algorithm and on selection of appropriate choice, only corresponding function will be executed
Insertion sort MUST properly use INSERT function
Selection sort MUST properly use FIND_MIN function