FUNCTIONS. Without return With return Without return With return. Example: function with arguments and with return value

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1 FUNCTIONS Definition: A is a set of instructions under a name that carries out a specific task, assigned to it. CLASSIFICATION of s: 1. User defined s (UDF) 2. Library s USER DEFINED FUNCTIONS Without arguments With arguments Without return With return Without return With return void sum( ) int sum( ) void sum(int,int) int sum(int,int) Example: without arguments and without return value without arguments and with return value with arguments and without return value with arguments and with return value Advantages: 1. It avoids the need for redundant programming of the same instructions. 2. Logical clarity of the programming will be clear. 3. Easy to debug. 4. A library with user defined s can be created. Function prototype: If we use any variable in the program, we declare that variable in the declaration section of the program. Similarly any that is to be called should be declared before its call in the calling. This declaration of a is called prototype. Function declaration should be done either in the declaration section of calling or before it. The prototype should agree with definition of that. Prototype contains the data type returned by the followed by the name of that and a pair of parentheses enclosing the data type of each parameter separately. Optionally the name of each parameter may be given. Ex: int fact(int); or int fact(int n); If there are no parameters, void should be shown in parentheses. Similarly if there is no return value, return value type should be indicated as void. Notes Prepared by T. Ratna Reddy. Associate Professor, CBIT Mobile Page 27

2 FUNCTION CALL Function call means, accessing a. A can be called by specifying its name, followed by a list of arguments enclosed in the parentheses, and separated by comma Example: f=fact(n); If a call does not require any arguments, an empty pair of parentheses must follow the name. A call may appear itself or it may be one of the operand within a expression. Example: printf( %d,fact(n)); Arguments in call, and formal parameters in declaration must be same in number, type and order. Difference between actual and formal parameters Variables used in calling are called actual parameters or arguments Variables used in definition are called formal parameters or dummy parameters or place holders. Parameter passing mechanisms There are two parameter passing mechanisms 1. call by value. Or passing by value 2. call by reference or passing by address or call by address. Call by value: Passing arguments by value means, the contents of the arguments in the calling are not changed, even if they are changed in the called. This is because the content of the variable is copied to the formal parameter of the definition, thus preventing the contents of the argument in the calling. Call by reference: Call by reference means sending the address of variables as arguments to the. When addresses are sent, the changes occurred in the called can also effect in the calling. /* example to illustrate call by value and call by reference*/ void makezero(int,int*); /* prototype*/ int x=50,y=100; makezero(x,&y); /* call by value and referene */ printf( x=%d y=%d, x,y); /* makezero */ void makezero(int a,int *b) a=0; *b=0; OUTPUT x=50 y=0 Notes Prepared by T. Ratna Reddy. Associate Professor, CBIT Mobile Page 28

3 Factorial of number by using long int fact(int); int n; long int f; printf("enter a number\n"); scanf("%d",&n); f = fact(n); printf("the factorial of %d is %ld",n,f); /*end of main */ /* fact*/ long int fact(int x) int i; long int f1=1; for(i=1;i<=x;i++) f1 = f1*i; return(f1); Fibonacci series by int n; void fib(int); printf( "\nhow many Fibonacci numbers required? "); scanf("%d", &n); printf("\nthe first %3d Fibonacci numbers are\n", n); fib(n); void fib(int n) int i, f1, f2, f3; f1 = f2 = 1; EXAMPLE PROGRAMS ON FUNCTIONS printf("%5d\n", f1); printf("%5d\n", f2); for( i = 3; i <= n; i++) f3 = f1 + f2; printf("%5d\n", f3); f1 = f2; f2 = f3; GCD of two numbers by int m,n,g; int gcd(int,int); printf("enter two numbers\n"); scanf("%d%d",&m,&n); g = gcd(m,n); printf("gcd of %d and %d is %d", m,n,g); /* End of main() */ int gcd(int m,int n) int r,g1; do r=m%n; if(r!=0) m=n; n=r; while(r!=0); */ g1=n; return(g1); /* End of gcd Notes Prepared by T. Ratna Reddy. Associate Professor, CBIT Mobile Page 29

4 RECURSIVE FUNCTIONS A which calls itself until a certain condition is reached is called recursive /* to find factorial of a number recursively */ int rfactorial(int); int n,f; printf("enter a number\n"); scanf("%d",&n); f=rfactorial(n); printf("factorial of %d is %d",n,f); /* factorial */ int rfactorial(int n) if(n==0) return 1; else return(n*rfactorial(n-1)); /* to find nth fib number recursively */ int rfib(int); int n,f; printf("enter a number\n"); scanf("%d",&n); f=rfib(n); printf("n th fibonacci number is %d",f); /* rfib */ int rfib(int n) if(n==1 n==2) return 1; else return(rfib(n-1)+rfib(n-2)); /* to find GCD of two numbers recursively */ int rgcd(int,int); int m,n,g; printf("enter two numbers\n"); scanf("%d%d",&m,&n); g=rgcd(m,n); printf("gcd is %d",g); /* rgcd */ int rgcd(int m,int n) if(m%n==0) return n; else return(rgcd(n,m%n)); /* to find ncr recursively */ int rncr(int,int); int n,r,s; printf("enter two numbers\n"); scanf("%d%d",&n,&r); s=rncr(n,r); printf("ncr =%d\n",s); int rncr(int n,int r) if(r==0 n==r) return 1; Notes Prepared by T. Ratna Reddy. Associate Professor, CBIT Mobile Page 30

5 else return(rncr(n-1,r)+rncr(n-1,r-1)); /* to find sum of digits recursively */ int rsum(int n); int n,s; printf("enter a number\n"); scanf("%d",&n); s=rsum(n); printf("sum of digits =%d\n",s); int rsum(int n) if(n==0) return n; else return(n%10+rsum(n/10)); /* to find the sum of two numbers recursively */ int rsum(int,int); int m,n,s; printf("enter two numbers\n"); scanf("%d%d",&m,&n); s=rsum(m,n); printf("sum =%d\n",s); int rsum(int m,int n) if(n==0) return m; else return(rsum(m+1,n-1)); Difference between iterative and recursive s Iterative 1. Function calls some other s 2. while loop, do while loop or for loop is necessary in iterative 3. Fast in execution since one call is enough to get the result Recursive 1. Function calls some itself 2. if statement is necessary in recursive 3. Slow in execution since several calls are involved to get the result, as number of increases execution will slow down. to value Eg: fact(4) = We require mathematical steps or procedure to write an iterative. 6. Stacks are not used during execution to another call Eg: fact(4) = 4 x fact(3) 5. We require a formula to write a recursive. 6. Stacks are used during execution of recursive s 4. Function call leads 4. Function call leads Notes Prepared by T. Ratna Reddy. Associate Professor, CBIT Mobile Page 31

6 STORAGE CLASSES Auto Stati Extern Register Normally the life of a variable is limited to a as long as the is alive. How to make it alive in a file or throughout the program or limiting only to a block inside a or to make common to a desired couple of s etc., The answer lies in STORAGE CLASSES or VARIABLE TYPES. There are four types of storage classes. 1. Automatic variables. 2. External variables. 3. Static variables. 4. Register variables. AUTOMATIC VARIABLES: Automatic variables are declared inside a, in which they are to be utilized. They are created when the is called and destroyed automatically when the is exited. By default all variables are automatic variables. These are also called local or internal variables. EXTERNAL VARIABLES Variables that are both alive and active throughout the entire program are called external variables. These variables are available to all s in that program. Whatever changes that occur in a, will effect the value of that variable. STATIC VARIABLES When a variable is declared as a static variable it is assigned the value zero. Static variables are initialized only once. They will not be initialized for second time during the program. When static is applied to a global variable, the global variable becomes inaccessible outside the file. REGISTER VARIABLES This is local to a or a block. If a compiler finds a physical register in the CPU free for the time being, and also big enough to hold the value, then it may stick that variable in that register. Otherwise the compiler treats that variable as ordinary. It is machine dependent. But compiler will not give error messages even if no register available in reserve. Notes Prepared by T. Ratna Reddy. Associate Professor, CBIT Mobile Page 32

7 If we know that a particular variable will be used often inside -say the variable inside a loop-then we can declare that variable with class register. So that the interaction will be very fast //Write a program to demonstrate life cycle of auto variable in nested blocks. auto int x=1; auto int x=2; auto int x=3; printf( %d\n, x); printf( %d\n,x); printf( %d\n,x); Output // program to illustrate automatic and external variables int x=1; int fun1() x=x+10; return x; int fun2() int x; x=20; return x; int fun3() x=1000; return x; int x=100; printf("% d\n",fun1()); printf("%d\n",fun2()); printf("% d\n",fun3()); x=0; printf("%d\n",x); printf("% d\n",fun1()); printf("%d\n",fun2()); printf("% d\n",fun3()); OUTPUT // program to illustrate static variable int fun(); int i; for(i=1;i<5;i++) printf("%d\n",fun()); int fun() static int x=0; x+=1; return(x); OUTPUT // program to illustrate register variable Notes Prepared by T. Ratna Reddy. Associate Professor, CBIT Mobile Page 32

8 Stroge Class Type Default initial value auto local Garbage value register int i; int i; for(i=1;i<1000;i++) printf("% d",i); Place of declaration Within or block Scope Only within the or block where it is declared life Until block is no longer active static local zero Until program ends extern global zero Head of all s within file All files including other files where declared extern While any file is active. terminates 5. It is lost when program terminates but not when terminates automatic variable static variable 1. It is declared by auto int a = 10; 1. It is declared by static int a = 10; 2. It must be declared inside the 2. It can be declared inside or outside the 3. If it is not initialized, garbage value is stored 4. It is initialized every time is called that is repeated initialization 5. It is lost when 3. If it is not initialized, zero is stored 4. It is initialized once and only one but not every time when is called Local variable 1. It is declaration inside the 2.It is declared by auto int a=10 or int a = 10 (auto is default scope) 3. If it is not initialized garbage value is Global variable 1.It is declaration outside the 2. It is declared by int a=10 3. If it is not initialized zero is stored Notes Prepared by T. Ratna Reddy. Associate Professor, CBIT Mobile Page 33

9 stored Eg: int a; a is garbage value 4. It is created when the starts execution and lost when the terminates 5. It is visible in only one. 6. It can be accessed in only one that is the where it is declared 7. Data sharing is not possible that is data of local variable can be accessed by only one 8. Parameters passing is required for local variable that is local variable of one variable 9. If value of local variable is modified in one changes are not visible in another s Eg: int a; a = 0 4. It is created before program execution starts and lost when program terminates 5. It is visible through out the program. 6. It can be accessed in more than one. 7. Data sharing is possible that is multiple s can access the same global variable. 8. Parameters passing is not required for global variable since global variable is visible throughout the program 9. If value of global variable is modified in one changes are visible in rest of the program Notes Prepared by T. Ratna Reddy. Associate Professor, CBIT Mobile Page 33

Unit III Functions. C functions can be classified into two categories, namely, library functions and user defined functions.

Unit III Functions. C functions can be classified into two categories, namely, library functions and user defined functions. Unit III Functions Functions: Function Definition, Function prototype, types of User Defined Functions, Function calling mechanisms, Built-in string handling and character handling functions, recursion,