11. Functions

Functions in C :

• functions are containers that help reduce duplicacy of code

• make code reusable at different positions in our program.

• Keeps program modular and seperates logic of program in seperate blocks.

Types of Functions :

1. User defined functions.

2. Built in functions.

Note : In reality in c programming only user defined functions exist but for writing in exams if you are in india, then write both types.

User Defined Functions :

These functions are defined by developer itself.

example :

    int max(int a, int b){
        return (a>b) ? a : b;
    }

Built in Functions :

These are the functions defined by creator of c and are used by developers.

example :

    int main() {
        //built in function
        printf("i am built in function of c");
        return 0;
    }

Function Invokation :

Steps to call a function in our program is called function invocation.

example:

    int main(){
        max(1, 3); // invoked max function
        return 0;
    }

Nested Function :

1. Nesting of functions is possible in c.

2. Nested functions are functions declared/invoked within other function functions.

Rules for Functions :

1. Variable name rules are same for function naming rules.

2. Function Arguments are optional.

3. Function return type could be void.

4. By default a function in c returns int as datatype.

5. return keyword is used to send response back from function.

Syntax of Function :

    return_type function_name( arguments )
    {
        // body of function.
    }

Examples of Function :

    //function returning void.
    void print_letters (char c)
    {
        for( int i = 0; i <= 10; i++)
        {
             printf("%c\n",c);
        }
    }

    // function return int as return type.

    int max( int a, int b )
    {
        return (a>b) ? a : b ;
    }

    // function with no arguments
    void drawcircle()
    {
        printf("I am drawing circle\n");
        circle(100,100,30);
    }

Function Arguments :

1. Actual Arguments

2. Formal Arguments

Formal Arguments :

These are the declarations within user defined functions.

example :

    int max( int a, int b ) // formal arguments.
    {
        return ( a > b ) ? a : b ;
    }

Actual Arguments :

These are values passed during invocation of function.

example :

    int main(){
        max( 2, 4 ); // actual arguments.
        return 0;
    }

Expression Evaluation in Function Invocation:

Expressions passed in functions are always evaluated form right to left.

example :

    int sum( int a, int b)
    {
        return a + b ;
    }

    int main()
    {
        int result = sum ( printf("abc"); , printf("def") );

        printf("\tResult is %d ", result );

        return 0;
    }

Output will be : defabc Result is 6

Expression evaluation in Function Definition :

• In case of function declaration expression evaluation does not exist.

• In case of function definition values are assigned/declared from left to right.

example :

    int multiply(int a, int b)
    {
        return a * b ;
    }

Some practice for functions :

Find Output of program :

    int max ( int a , int b )
    {
        return ( a > b ) ? a : b ;
    }

    int main()
    {
        int number = 10;
        int result = max ( ++a , ++a ); // result = ?
        return 0;
    }

Find Max of four numbers :

    int max ( int a, int b )
    {
        return ( a > b ) ? a : b ;
    }

    int main()
    {
        int first = 10;
        int second = 12;
        int third = 20;
        int fourth = 22;

        // code for max.
        int result = max( max(first, second) , max(third, fourth) ) ;
        printf(" Maximum value is %d \n", result ) ;
        return 0;
    }

Program to print letters in increasing order.

    void pattern(char c, int times)
    {
        for(int i = 0; i <= times; i++){
            for(int j =0; j <= i; j++){
               printf("%c",c);
            }
           printf("\n");
        }
    }

    int main()
    {
        pattern('$', 5);
        pattern('Û', 7);
        return 0;
    }