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

Size: px

Start display at page:

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

Shanon Lewis
6 years ago
Views:

1 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, Storage Classes, multi-file compilation, Function with Arrays. C functions can be classified into two categories, namely, library functions and user defined functions. User defined functions has to be developed by the user at the time of writing a program. Function is a self contained block of code that performs a particular task. Need for user defined functions or Advantages of user defined function: 1. The program will be easier to understand, maintain and debug. 2. Reusable codes that can be used in other programs. 3. A large program can be divided into smaller modules. Hence, a large project can be divided among many programmers. Function prototype or function declaration: Function must be declared before it is used in any program, same as a variable must be declared before it is used. This declaration is called function prototype or function declaration. return type function_name (arguments list); Here, i. return type is any valid data type, ii. function name is any valid 'C' name, iii. argument list contains data type of arguments separated with comma (,) if more than one argument is present in the list. Syntax for function definition: return_type function_name(argument list) statements; return ; //optional Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 1

2 Example program to explain in detail about function: int cube(int); // function prototype int x,c; printf("enter x to compute cube\n"); scanf("%d",&x); c=cube(x); // calling function, call by value, and x is actual argument or parameter printf("cube of %d = %d\n",x,c); int cube(int n) //Function Header, n is formal argument Function Definition or called function return n*n*n; A function must follow the same rules of formation of variable names in C. In the function prototype, argument list contains data types separated with comma with optional variable names and this statement ends with semicolon. In the calling function, only variable names are used along with the function name and ends with semicolon. When the compiler encounters a function call, the control is transferred to the function definition. This function is then executed line by line and a value is returned when the return statement is encountered. In the called function or function definition, variable names along with their data types are used. Open and close curly braces are used to define a block of statements. And an optional return statement is used in the function definition. If any data type is specified in the return type part, it is necessary to use return statement to return a quantity to the calling function. This situation arises when the value returned is based on certain conditions. For example, in Linear search function, for(i=0;i<n;i++) if(a[i]==ele) return i; return -1; Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 2

3 In this example, if the given search element is present in the input array, then that element s position is returned. If that element is not present in the input array, -1 is returned. A function may have more than one return statement Here, Actual arguments are included in the function calling part. Formal arguments are dummy arguments means actual argument values are just copied into these formal arguments. Types of user defined functions: 1. Functions with no arguments and no return value. 2. Functions with arguments and no return value. 3. Functions with no arguments and return value. 4. Functions with arguments and return value. Functions with no arguments and no return value: void printline(); printf("name\t\troll Number\n"); printline(); printf("anuradha\t1001\nsasi Latha\t1003\n"); printline(); void printline() int i; for(i=1;i<=40;i++) printf("-"); printf("\n"); Functions with arguments and no return value: //Product of prime integers from 1 to N //return type functionname (arguments list); Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 3

4 void primeprod(int); // Function prototype int n; printf("enter n\n"); scanf("%d",&n); primeprod(n); // Function calling void primeprod(int n) // Function Definition int i,j,cnt,p; for(i=1,p=1;i<=n;i++) for(j=1,cnt=0;j<=i;j++) if(i%j==0) cnt++; if(cnt==2) p=p*i; printf("product of prime integers=%d\n",p); Functions with no arguments and return value: //Product of non-prime integers from 1 to N int nprimeprod(); printf("product of non-prime integers=%d\n",nprimeprod()); int nprimeprod() int i,j,cnt,p; int n; printf("enter n\n"); scanf("%d",&n); for(i=1,p=1;i<=n;i++) for(j=1,cnt=0;j<=i;j++) if(i%j==0) cnt++; Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 4

5 if(cnt!=2) p=p*i; return(p); Functions with arguments and return value: //Factorial of given number int fact(int),f; int n; printf("enter n\n"); scanf("%d",&n); f=fact(n); printf("factorial of %d = %d\n",n,f); int fact(int n) int i,f; for(i=1,f=1;i<=n;i++) f=f*i; return f; // Fib term or not int n; void fibterm(int); printf("enter n\n"); scanf("%d",&n); fibterm(n); void fibterm(int n) int a,b,c; if(n==0 n==1) Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 5

6 printf("%d is fib term\n",n); return; for(a=0,b=1,c=0;c<=n;) c=a+b; a=b; b=c; if(c==n) printf("%d is fib term\n",n); break; if(c>n) printf("%d is not fib term\n",n); Function calling mechanisms: A function can be called in two ways: a. call by value. b. call by reference. Call by value: Actual arguments are included in the function calling part. Formal arguments are dummy arguments means actual argument values are just copied into these formal arguments, any changes made to these formal arguments are not reflected to the calling function. Because by default function is called by call by value. void swap(int,int); int a,b; printf("enter a,b values\n"); scanf("%d%d",&a,&b); printf("a,b values before swap function a=%d\tb=%d\n",a,b); swap(a,b); printf("\na,b values after swap function a=%d\tb=%d\n",a,b); Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 6

7 void swap(int x,int y) int t=x; x=y; y=t; Enter a,b values 4 5 a,b values before swap function a=4 b=5 a,b values after swap function a=4 b=5 Call by reference: By using call by value only one value is return to calling function by explicitly use the return statement. There are situations to return more than one value to calling function. This is achieved by using call by reference mechanism. Actual arguments are included in the function calling part by passing the addresses of variables a, b are passed as arguments to function and received as pointers. Any changes made to these arguments are directly modified in their address locations, so returned to the calling function. void swap(int*,int*); int a,b; printf("enter a,b values\n"); scanf("%d%d",&a,&b); printf("a,b values before swap function a=%d\tb=%d\n",a,b); swap(&a,&b); printf("\na,b values after swap function a=%d\tb=%d\n",a,b); void swap(int *x,int *y) int t = *x; *x = *y; *y = t; Enter a, b values Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 7

8 a, b values before swap function a=10 b=20 a, b values after swap function a=20 b=10 Function with Arrays: When an array is passed as argument to a function, then by default array is passed as reference. Because the base address of an array is passed to the function definition. So, any changes made to that array are reflected to the calling function without using return statement. Example program to sort given array elements using bubble sort by passing array as argument to bsort function. void bsort(int [20],int); int n,i,a[20]; printf("enter no. of elements\n"); scanf("%d",&n); printf("enter array elements\n"); for(i=0;i<n;i++) scanf("%d",&a[i]); bsort(a,n); //calling function printf("elements after sorting\n"); for(i=0;i<n;i++) printf("%d\t",a[i]); printf("\n"); void bsort(int a[20],int n) // function definition int i,j,t; for(i=0;i<n-1;i++) for(j=0;j<n-i-1;j++) if(a[j]>a[j+1]) t=a[j]; a[j]=a[j+1]; a[j+1]=t; Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 8

9 enter no. of elements 5 enter array elements Elements after sorting After completion of bsort function, the resultant sorted elements are displayed in main function without using any return statement in the called function. The elements are in sorted order. Recursion: A function that calls itself is known as a recursive function. And, this technique is known as recursion. Recursion function must contain termination condition otherwise it will go into an infinite loop Recursive functions are very useful to solve many mathematical problems, such as calculating the factorial of a number, generating Fibonacci series, etc. Sum of n natural numbers using recursion: How recursion internally works: Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 9

10 Advantages and Disadvantages of Recursion Recursion makes program neat and cleaner. All algorithms can be defined recursively which makes it easier to visualize and prove. If the speed of the program is vital then, you should avoid using recursion. Recursions use more memory and are generally slow. Instead, you can use loop. // Binary search using recursion (previous paper question): int bsearch(int [20],int,int,int); void bsort(int [20],int); int n,i,a[20],pos,ele; printf("enter no. of elements\n"); scanf("%d",&n); printf("enter array elements\n"); for(i=0;i<n;i++) scanf("%d",&a[i]); bsort(a,n); printf("elements after sorting\n"); for(i=0;i<n;i++) printf("%d\t",a[i]); printf("\nenter element to search\n"); scanf("%d",&ele); pos=bsearch(a,0,n-1,ele); if(pos!=-1) printf("\n%d element found in %d position\n",ele,pos); else printf("\n %d element not found\n",ele); void bsort(int a[20],int n) int i,j,t; for(i=0;i<n-1;i++) for(j=0;j<n-i-1;j++) if(a[j]>a[j+1]) t=a[j]; a[j]=a[j+1]; Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 10

11 a[j+1]=t; int bsearch(int a[20],int low,int high,int ele) int mid; while(low<=high) mid=(low+high)/2; if(a[mid]==ele) return mid; else if(ele<a[mid]) return bsearch(a,low,mid-1,ele); else return bsearch(a,mid+1,high,ele); enter no. of elements 5 enter array elements Elements after sorting Enter element to search element found in 3 position // Factorial of a number using recursion int fact(int),f; int n; printf("enter n\n"); scanf("%d",&n); f=fact(n); printf("factorial of %d = %d\n",n,f); Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 11

12 int fact(int n) if(n==0 n==1) return 1; else return n*fact(n-1); enter n 4 Factorial of 4 = 24 Factorial recursive function working: Assume n=4. Since the value of n is not 1, the statement return n*fact(n-1); will be executed with n=4. That is, return 4 * factorial(3); will be evaluated. The expression on the right-hand side includes a call to factorial with n = 3. This call return the following value: 3 * fact(2); Once again, fact function is called with n = 2. This time, the function returns 2*fact(1); Once again, fact function is called with n = 1. This time, the function returns 1. The sequence of operations can be summarized as follows: return 4 * fact(3) return 4 * 3 * fact(2) return 4 * 3 * 2 * fact(1) return 4 * 3 * 2 * 1 return 24 Recursive functions can be effectively used to solve problems where the solution is expressed in terms of successively applying the same solution to subsets of the problem. When recursive functions are used, it must have an if statement somewhere to force the function to return without the recursive call being executed. Otherwise, the function will never return. Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 12

13 // Fibonacci series using recursion int i,n; int fib(int); printf("enter n\n"); scanf("%d",&n); for(i=0;i<n;i++) printf("%d\t",fib(i)); int fib(int n) if(n==0 n==1) return n; else return fib(n-1)+fib(n-2) ; enter n //gcd using recursion int int a,b; int gcd(int,int); printf("enter 2 numbers:"); scanf("%d%d",&a,&b); printf("greatest Common Divisor is %d",gcd(a,b)); return 0; int gcd(int a,int b) if(b==0) return a; else return gcd(b,a%b); Enter 2 numbers: Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 13

14 8 6 Greatest Common Divisor is 2 Storage classes: The storage class determines the part of memory where storage allocated for a variable and how long the storage allocation continues to exist. Scope: The scope of variable determines over what part(s) of the program a variable is actually available for use. (active) or The region of a program in which a variable is available for use. Visibility: The program s ability to access a variable from the memory. Lifetime: The lifetime of a variable is the duration of time in which a variable exists in the memory during execution. Local variables: Local variables are accessed only in a block where those variables are declared. Example: void local1(); void local2(); int m=1; local1(); printf("in main m=%d\n",m); void local1() int m=11; local2(); printf("in local1 m=%d\n",m); void local2() int m=22; printf("in local2 m=%d\n",m); Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 14

15 In local2 m=22 In local1 m=11 In main m=1 Global variables: Once a variable has been declared as global, any function can use it and change its value. Then, subsequent functions can reference only that new value. Global variables are initialized to zero by default. Global variable is that it is visible only from the point of declaration to the end of the program. Example: void global1(); void global2(); int m=10; global1(); m=m+1; printf("in main m=%d\n",m); void global1() global2(); m=m+11; printf("in global1 m=%d\n",m); void global2() m=m+22; printf("in global2 m=%d\n",m); In global2 m=32 In global1 m=43 In main m=44 Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 15

16 Storage classes are of 4 types: 1. Automatic variables 2. Static variables 3. Register variables 4. External variables Storage specifier auto static register extern Description Storage place: CPU Memory Initial value: garbage Scope: local Lifetime: within the function only Storage place: CPU Memory Initial value: zero Scope: local Lifetime: Retains the value of the variable between different function calls. Storage place: CPU Registers Initial value: garbage Scope: local Lifetime: with in the function only Storage place: CPU Memory Initial value: zero Scope: global Lifetime: Till end of the main program. Variable definition might be anywhere in the C program. Automatic variables: int i; void autov(); for(i=1;i<=3;i++) autov(); void autov() auto int x=0; x=x+1; printf("x=%d\n",x); Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 16

17 x=1 x=1 x=1 When i=1, autov() function is called for 1 st time: Because of the initial value of the automatic variables is garbage, explicitly assigning 0 to x. When x=x+1, x is incremented by 1. Then x=1 is printed. When i=2, autov() function is called for 2 nd time: Because Automatic variable s life time is local and initial value of the automatic variables is garbage, again explicitly assigning 0 to x. When x=x+1, x is incremented by 1. Then x=1 is printed. Static variables: int i; void staticv(); for(i=1;i<=3;i++) staticv(); void staticv() static int x; x=x+1; printf("x=%d\n",x); x=1 x=2 x=3 When i=1, staticv() function is called for 1 st time: Because of the initial value of the static variables is zero (0), there is no need to explicit assignment of x. When x=x+1, x is incremented by 1. Then x=1 is printed. When i=2, staticv() function is called for 2 nd time: Because of static variable s life time is throughout the program, x value is retained as 1. When x=x+1, then x=1+1=2. Then x=2 is printed. Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 17

18 Register variables: register int i; void regv(); for(i=1;i<=3;i++) regv(); void regv() register int x=0; x=x+1; printf("\nx=%d",x); x=1 x=1 x=1 When i=1, regv() function is called for 1 st time: Because of the initial value of the register variables is garbage, explicitly assigning 0 to x. When x=x+1, x is incremented by 1. Then x=1 is printed. When i=2, regv() function is called for 2 nd time: Because Register variable s life time is local and initial value of the automatic variables is garbage, again explicitly assigning 0 to x. When x=x+1, x is incremented by 1. Then x=1 is printed. Extern variables: extern int y; // external declaration void globe1(); void globe2(); globe1(); y=y+10; printf("in main y=%d\n",y); globe2(); Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 18

19 void globe1() y=y+1; printf("in globe1 y=%d\n",y); int y; //definition void globe2() y=y*5; printf("in globe2 y=%d\n",y); In globe1 y=1 In main y=11 In globe2 y=55 Here, y is a global variable and by default initial value of global variable is zero (0). But global variable y is declared after the and globe1() functions. So, y is unavailable to those two functions even it is declared as global variable. That variable y is made available to those two functions by declaring that variable as external variable. extern int y; //external declaration (no memory is allocated to this variable). This declaration informs the compiler, that y is declared as external variable and that variable is declared as a global variable somewhere in the program. int y; //definition When this statement is encountered in the program, compiler allocates memory to that variable. Multi file compilation: // Contents of file1.c extern int m; void externf(); int i=10; m=m+50; printf("in main i=%d\tm=%d\n",i,m); externf(); externf2(); Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 19

20 externf1(); void externf() int j=11; m=m*5; printf("externf m=%d\tj=%d\n",m,j); //file2.c int m; void externf1() int k=111; m=500; printf("in extern f1 m=%d\tk=%d\n",m,k); void externf2() int l=222; m=1000; printf("in extern f2 m=%d\tl=%d\n",m,l); In the file1.c, 'm' is declared as external variable; here no memory is allocated to that variable 'm'. And that variable is globally defined in another file file2.c. That variable 'm' is made available to the file1.c by compiling these two files at the same time. //Compilation $cc file1.c file2.c $./a.out In main i=10 m=50 Externf m=250 j=11 In extern f2 m=1000 l=222 In extern f1 m=500 k=111 Prepared by Aravinda Kasukurthi, CSE, RVRJCCE 20

int Return the number of characters in string s.

int Return the number of characters in string s. 1a.String handling functions: Function strcmp(const char *s1, const char *s2) strcpy(char *s1, const char *s2) strlen(const char *) strcat(char *s1, Data type returned int Task Compare two strings lexicographically.