Functions Introduction to Programming By Engr. Bilal Ahmad 1ITP by Engr. Bilal Ahmad

Functions  It allows to structure programs in segments of code to perform individual tasks.  In C++, a function is a group of statements that is given a name, which can be called from some point of the program.  The most common syntax for a function is; Type name (parameter1, parameter2,……..) { Statements } 2ITP by Engr. Bilal Ahmad

Explanation  Type is the type of the value returned by this function  Name is the identifier by which the function will be called  Parameters as many as you would like, each parameter must consist of the type followed by an identifier, with each parameter being separated by a comma. For example int x, here int is the type and x is the identifier.  Statements is the functions body. It is the block of the statements surrounding by the braces { } that specify where the function actually does. 3ITP by Engr. Bilal Ahmad

Example  // function example  #include  using namespace std;  int addition (int a, int b)  {  int r;  r=a+b;  return r;  }   int main ()  {  int z;  z = addition (5,3);  cout << "The result is " << z;  }  The result is ? 4ITP by Engr. Bilal Ahmad

Explanation  The program is divided in two functions;  Addition and main  Remember that no matter the order in which they are defined  A C++ program always start by calling the main function  In fact main is the only function that is called automatically  The code in any other function is only executed if its function is called from the main otherwise the function has no significance 5ITP by Engr. Bilal Ahmad

Example’s Explanation  Lets have some discussion about the example that we have done before. What we did we created the addition function right?  Can you identify the type, name and parameters etc. in the example below; 6ITP by Engr. Bilal Ahmad

What is return?  The final statement you all have seen is the return statement do you have any idea why it is used?  This statement is used to send the control back to the main function so that the function can be used for other processing  In the example the return r with have the value of 8 and than will pass on the control to the main function. 7ITP by Engr. Bilal Ahmad

Can a function be called multiple times within a program?  // function example  #include  using namespace std;   int subtraction (int a, int b)  {  int r;  r=a-b;  return r;  }   int main ()  {  int x=5, y=3, z;  z = subtraction (7,2);  cout << "The first result is " << z << '\n';  cout << "The second result is " << subtraction (7,2) << '\n';  cout << "The third result is " << subtraction (x,y) << '\n';  z= 4 + subtraction (x,y);  cout << "The fourth result is " << z << '\n';  } 8ITP by Engr. Bilal Ahmad

Functions with NO types  You will use void in this case  The syntax is type name (argument1, argument2….) {statements}  Requires the declaration to begin with a type because it is the syntax requirement.  If there is a function that doesn’t need to return a value what will you do? Is there any function where there is no need to return a value. remember the first program that we did to start with the C++ Code! 9ITP by Engr. Bilal Ahmad

Example  // void function example  #include  using namespace std;   void printmessage ()  {  cout << "I'm a function!";  }   int main ()  {  printmessage ();  } 10ITP by Engr. Bilal Ahmad

Quiz  You have 10 minutes maximum to attempt this quiz.  On a blank piece of paper just write your name and roll number and without any other information just write the output of the code.  No copying No cheating  After 10 minutes there will be no marking of your quiz, I am sorry.  The functions will be ended with this quiz, if you need any further information you can read ITP by Engr. Bilal Ahmad

Quiz  #include  using namespace std;  int divide (int a, int b=2)  {  int r;  r=a/b;  return (r);  }  int main ()  {  cout << divide (12) << '\n';  cout << divide (20,4) << '\n';  return 0;  } 12ITP by Engr. Bilal Ahmad

Surprise At the End of the Lecture there will be a surprise for you all. Stay tuned 13ITP by Engr. Bilal Ahmad

Arrays  So now we have started writing functions, which will become a part of our every program.  As C language is an Function Oriented Language so we will be dealing with too many functions, not in this ITP course but OOP and DSA.  Our program tool kit is almost complete but still a very important component is missing and it is called Arrays. This Lecture will be based on Arrays. I will strongly advise you after this Lecture go and read Lecture 11 of CS201-ITP can be found on ITP by Engr. Bilal Ahmad

Why Arrays?  Let us consider an Example to calculate the average of 10 students. At first we will declare 10 variables to store the age of 10 students each and then sum up all the ages and divide them with 10. complicated process isn’t it. If yes than can you suggest any other way?  No because you don’t Know  I know ‘Yes’ but why shall I tell you all?  Acha koi nahi batata hun next slide dekho ap sab 15ITP by Engr. Bilal Ahmad

Arrays Explanation  Array is a special data type. Suppose if you have 100 students and you want to calculate the average instead of declaring 100 variables you use the simple and straight forward arrays.  Declaration is simple Data_type array_name [size]; for example Int ages [10]; 16ITP by Engr. Bilal Ahmad

Structure of Array 17ITP by Engr. Bilal Ahmad

Sample Problem 1  Problem Statement: Write a Program which reads positive integers from the user and store these ones in an array. User can enter a maximum of 100 numbers. Stop taking inputs when user enters -1 18ITP by Engr. Bilal Ahmad

Solution  We have to declare an integer array of size 100  We need to use a loop to get the input from the users  There are two conditions to terminate the loop and they are either user has entered 100 numbers or user entered -1  For and while loop can execute zero or more times whereas do while may execute one or more times  We take an integer z to get the input from the user and small I as a counter so the condition will be (z!-1 && i< 100) 19ITP by Engr. Bilal Ahmad

Program Code  # include  using namespace std;  main ()  {  int c[100];  int i,z;  do  {  int z, i = 0;  cout<<"please enter the number (-1 to endup the input)"<<endl;  cin >> z;  if (z!= -1)  {  c[i]=z;  }  i++;  }  while  (z!=-1 && i< 100);  cout <<"the total number of positive integers entered by user is"<<i - 1;  }  20ITP by Engr. Bilal Ahmad

Surprise  Well it is not any prize for the surprise but it was the Last Lecture to cover the course content, in case if we get some time we will try to have some labs but your course is completed. Read till chapter no 12 of the Book uploaded on  It was a pleasure to have all you in my class and I think so I have done my level best to give you a nice experience in the University. I would like you to write a 1 page document and share all your experiences with me. I will mark it for your assignment as well, it will be a treat for you. Be positive and write whatever you want related to me as a person, course etc. 21ITP by Engr. Bilal Ahmad

 You all are very dear and highly respectful for me and I wish you all the very best of Luck for the future.  You are not going to have any courses with me in the next semester but if I am in the University you will face me in semester 6 to high onwards.  May Allah bless you all “AMEEN”. If you need any help/ advise let me know and I will be there for you, even if I am not in the University you can do so.  Good Luck again and all the best for the examination. I believe that you all have potential and you all will get good grades.  At the end we all are human beings if you are hurt because of me I am sorry for that.  If you want to say any thing for me feel free and I am listening. 22ITP by Engr. Bilal Ahmad