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User defined function in c
- 2. INTRODUCTION • C functionscan be classified into two categories – Library functions – User-defined functions
- 3. LIBRARY FUNCTIONS – Libraryfunctions are not required to be written by – printf and scanf belong to the category of library function – sqrt, cos, strcat, etc are some of library functions
- 4. USER-DEFINED FUNCTIONS – User-definedfunctions has to be developed by the user at the time of writing a program – A user-defined functions can later become a part of the C program library – main is an example of user-defined functions
- 5. ELEMENTS OF USER-DEFINED FUNCTIONS Thereare three elements related to functions – Function definition – Function call – Function declaration • The function definition is an independent program module that is specially written to implement the requirements of the function. • To use this function we need to invoke it at a required place in the program. This is known as the function call. • The program that calls the function is referred to as the calling program or calling function. • The calling program should declare any function that is to be used later in the program. This is known as the function declaration or function prototype.
- 6. FUNCTION DECLARATION A functiondeclaration consists of four parts – Function type (return type) – Function name – Parameter list – Terminating semicolon Syntax, Function-type function-name (parameter list); Example, void display(int);
- 7. FUNCTION DEFINITION A functiondefinition, also known as function implementation shall include the following elements; – Function name; – Function type; – List of parameters; – Local variable declaration; – Function statements; and – A return statement.
- 8. Syntax is….. function_type function_name(parameterlist) { local variable declaration; executable statement1; executable statement2; ---------------- ---------------- return(expression); }
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- 10. CALLING A FUNCTION Afunction can be called by simply using the function name in a statement When the function encounters a function call, the control is transferred to the function mul(x,y)
- 11. Example program main() { int p; p= mul(10,5); printf("%dn", p); } int mul(int x,int y) { int p; /*local variables*/ p = x * y;/* x = 10, y = 5*/ return(p); }
- 12. CATEGORY OF FUNCTIONS Category1: Functions with no arguments and no return values Category 2: Functions with arguments and no return values Category 3: Functions with arguments and one return values Category 4: Functions with no arguments but return a value
- 16. Function with noarguments and with return Values Main() data_type func1() { { ………….. …………… ………….. …………… C=func1(); …………… ………….. ……………. …………... Return(a); }
- 17. RETURNING A VALUE •C function returns a value of the type int as a default case when no other type is specified explicitly. return(value); Return the integer value of sum