Functions in C SHARDA UNIVERSITY. Presented By: Pushpendra K. Rajput Assistant Professor

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1 Functions in C Presented By: Pushpendra K. Rajput Assistant Professor 1

2 Introduction Call a mechanic You face a problem in your car It repeats many times. No need to instruct Continue with your job Mechanic will do its job. Mechanic knows his job 2

3 Introduction Callee (Require prior Information about mechanic i.e. Mobile number or Shop Number) Your activity is temporarily suspended Called Continue with your activity Mechanic s job over Mechanic s function wake up. No need to instruct Somebody trained him (Its job is predefined) 3

4 Introduction #include<stdio.h> #include<conio.h> void message(); //function declaration main() //calling function Execution of main starts message(); //function call Execution of main suspended printf( \n hello..this is main. ); Execution of main resumed message() //function definition Execution of message starts //called function printf( \n this is function ); Execution of message completed Output: this is function hello..this is main. 4

5 Functions A C program is made up of one or more functions, one of which is main( ). Execution always begins with main( ), no matter where it is placed in the program. By convention, main( ) is located before all other functions. When program control encounters a function name, the function is called (invoked). Program control passes to the function. The function is executed. Control is passed back to the calling function. 5

6 Functions A function is a self contained block of statements that perform a coherent task of some kind. It similar to hiring a person to perform a specific task. Functions make programs easier to understand. Functions can be called several times in the same program, allowing the code to be reused. A complex problem is often easier to solve by dividing it into several smaller parts, each of which can be solved by itself. This is called structured programming 6

7 Function Input and Output 7

8 Creating and using a function Function Declaration Function Calling Function Definition 8

9 Function Declaration Also called function prototype. It should be written before main(). The function prototype declares the input and output parameters of the function. The function prototype has the following syntax: <ret-type> <function name>(<parameter-list>); void/any data type that is supported by C (default int) a parameter should be declared separately (int x, int y) Example: A function that returns the absolute value of an integer is: int absolute(int x); 9

10 Function Call A function call has the following syntax: <function name>(<argument list>); Execution of called function starts from this statement Example: int distance = absolute(-5); 10

11 Function Definition A function definition has the following syntax: <ret-type> <function name>(<parameter list>) <local declarations> <sequence of statements> For example: Definition of a function that computes the absolute value of an integer: int absolute(int x) if (x >= 0) return x; else return -x; 11

12 Example #incllude<stdio.h> #include<conio.h> void italy(); void brazil(); void argentina(); void main() printf( \n I m in main ); italy(); brazil(); argentina(); printf( \n I am finally in main ); OUTPUT I am in main I m in italy I m in brazil I m in Argentina I am finally in main void italy() printf( \n I m in italy ); void brazil() printf( \n I m in brazil ); void argentina() printf( \n I m in Argentina ); 12

13 Functions cont.. Any function can be called from any other function. Any function can be called any number of times. No relation between order of definition and calling. A function can call itself(recursion) A function can not be defined in another function 13

14 Passing Values between Functions Communication between calling and called functions. The mechanism used to convey information to the called function is the argument (Parameter)- input to called function The mechanism used to convey information to the calling function is the return value - output from called function 14

15 Example int calsum(int x, int y, int z); void main() int a, b, c, sum; printf( \nenter any three numbers: ); main receives three scanf( %d%d%d, &a,&b,&c); values from keyboard main convey this info to calsum sum=calsum(a,b,c); calsum returns the result to main printf( \n Sum= %d, sum); & Main receives the result in sum variable int calsum(int x, int y, int z) int d; d=x+y+z; return(d); Calling- main() Called- calsum() 15

16 Example int calsum(int x, int y, int z); void main() int a, b, c, sum; printf( \nenter any three numbers: ); scanf( %d%d%d, &a,&b,&c); sum=calsum(a,b,c); printf( \n Sum= %d, sum); int calsum(int x, int y, int z) int d; d=x+y+z; return(d); Calling- main() Actual Arguments (a, b, c) Formal Arguments (x, y, z) Called- calsum() 16

17 return Statement On executing the return statement, it immediately transfers the control back to the calling function. It returns the value present after return There may be more than one return statements It may be in the middle of called function 17

18 Examples WAP to calculate the area and circumference of a circle using functions. User will enter the radius. Convert this program with a single function that can perform both the things according to user choice. 18

19 Example If the value of formal arguments is changed in the called function, the corresponding change does not take place in the calling function. void main() int a =30; fun(a); printf( \n%d,a); fun(int b) Output: 90 b=b+60; printf( \n%d,b); The values present in actual arguments are not physically moved to the formal arguments; just a copy of values in actual argument is made into formal arguments 30 19

20 Call by value Types of Function calls Call by reference Means arguments can be passed to a function in one of the two ways: a) sending values of the arguments b) sending addresses of the arguments

21 Pointers Pointer is a variable that contains address of another variable. Consider the declaration: int i=3; main() int i=3; printf( \naddress of i=%u,&i); printf( \nvalue of i=%d,i); i 3 Format specifier for unsigned int Location name Value at location Location number Address of

22 Address of i=65825 value of i=3 void main() int i=3; printf( \naddress of i=%u,&i); printf( \nvalue of i=%d,i); printf( \nvalue of i=%d,*(&i)); Address of i=24524 value of i=3 value of i=3 i Value at address Location name Value at location Location number

23 j=&i; i j But, we need to declare int *j; means value at address contained in j is an int 23

24 Main() int i=3,*j, **k; j=&i; k=&j; Illustration printf( \n Address of i=%u,&i); printf( \n Address of i=%u,j); printf( \naddress of i=%u,*k); printf( \naddress of j=%u,&j); printf( \naddress of j=%u,k); printf( \naddress of k=%u,&k); printf( \nvalue at j=%u,j); printf( \nvalue of k=%u,k); printf( \nvalue of i=%d,i); printf( \nvalue of i=%d, *(&i)); printf( \n Value of i=%d, *j); printf( \n value of i= %d, **K); i j k

25 Call by Value In this method, the value of actual arguments in the calling function is copied into corresponding formal arguments of the called function. Thus, the changes made to formal arguments in the called function have no effect on the values of actual arguments in the calling function.

26 Illustration void main() int a=10, b=20; swapv(a,b); printf( \na=%d b= %d, a,b); swapv(int x, int y) int t; t=x; x=y; y=t; printf( \nx=%d y=%d,x,y); Output: X=20 y=10 A=10 b=20 26

27 Call by Reference In this method, the addresses of actual arguments in the calling function are copied into formal arguments of the called function. This implies that using these addresses we would have an access to the actual arguments and hence we would be able to manipulate them.

28 28 SHARDA Illustration void main() int a=10, b=20; swapr(&a,&b); printf( \n a=%d b= %d, a,b); swapr(int *x, int *y) int t; t=*x; *x=*y; *y=t; Output: A=20 b=10

29 Intelligent use of Call of Reference void main() int radius; float area, perimeter; printf( \nenter radius of a circle: ); scanf( %d, &radius); areaperi(radius, &area, &perimeter); printf( Area=%f, area); printf( \n Perimeter=%f,perimeter); areaperi(int r, float *a, float *p) *a=3.14*r*r; *p=2*3.14*r; Output: Enter radius of a circle: 5 Area= Perimeter=

30 Array of pointers Similar to array of ints or array of floats. Since a pointer variable always contains address, an array of pointer would be nothing but a collection of addresses. The addresses present in a array of pointers can be addresses of isolated variables or addresses of array elements or any other addresses

31 Example void main() int *arr[4]; // array of integer pointers int i=31, j=5, k=19, l=71, m; arr[0]=&i; arr[1]=&j; arr[2]=&k; arr[3]=&l; for(m=0;m<=3;m++) printf( %d, *(arr[m]));

32 Recursion A function is called recursive, if a statement within the body of a function calls the function. Recursion is also known as the process in which something is defined in terms of itself. A FUNCTION WHICH CALLS ITSELF.

33 Definition A function is said to be recursively defined if the function definition refers to itself. It must have the following two properties: 1. There must be certain arguments, called base values for which the function does not refer to itself. 2. Each time the function does refer to itself, the argument of the function must be closer to base value.

34 Example (Factorial) Definition: a. if n = 1, then n! = 1 b. If n > 1, then n! = n. (n-1)! a) Base value is 0

35 Problem Write a program to find factorial of a given integer number:

36 Solution: (Non recursive) void main() int a, fact; printf( \n Enter a number: ); scanf( %d,&a); fact=factorial(a); printf( Factorial value=%d, fact); factorial(int x) int f=1, i; for(i=x; i>=1;i--) f=f*i; return (f);

37 Solution: (Recursive) void main() int a, fact; printf( \n Enter a number: ); scanf( %d, &a); fact=rec(a); printf( factorial value=%d,fact); rec(int x) int f; if(x==1) return(1); else f=x*rec(x-1); return(f); 37

38 Example (Fibonacci Series) Definition: a. if n = 0 or n = 1, then F n = n b. If n > 1, then F n = F n-2 + F n-1 a) Base values are 0 and 1

39 Thank You!!

Pointer in C SHARDA UNIVERSITY. Presented By: Pushpendra K. Rajput Assistant Professor

Pointer in C SHARDA UNIVERSITY. Presented By: Pushpendra K. Rajput Assistant Professor Pointer in C Presented By: Pushpendra K. Rajput Assistant Professor 1 Introduction The Pointer is a Variable which holds the Address of the other Variable in same memory. Such as Arrays, structures, and