Difference between revisions of "C-and-C++/C2/Functions/English"

What is a function

Syntax of function

Significance of return statement

Few examples on functions

We will also see some common errors and their solutions.

Ubuntu Operating system version 11.10

gcc and g++ Compiler version 4.6.1 on Ubuntu

A function is a self-contained program executing a specific task

Every program consists of one or more functions

Once it is executed the control will be returned back from where it was accessed

ret_type fun_name(parameters)

Or

ret_type fun_name( )

ret-type defines the type of data that the function returns

fun_name defines the name of the function

parameters is the list of variable names and their types

This is called as functions without arguments.

This is called as functions with arguments.

I have already typed the program on the editor

So i will just open it

function.c

and I have saved the file with the extentsion .c

Let me explain the code now

#include <stdio.h>

void add()

Here we have declared a function called add

Note that add function is without any arguments

And the return type is void

User-defined that is our add function

Pre-defined that is printf and main function

int a = 2;

int b = 3;

int c = a + b;

Then we add the values of a and b

The result is stored in c

printf("Value of C is %d\n",c);

void main()

add();

The addition operation will be performed and the result will be printed.

Now let us execute the program

gcc function.c -o fun

Type

./fun

gcc function.c -o fun

To execute, type

./fun

Output

Sum of a and b is 5

Functions contains special identifiers called as parameters or arguments

Let us see the same example with arguments

int add(int a, int b)

Type

int add(int a, int b)

Here we have declared a function called add

int a and int b are the arguments of the function add

int a=2;

int b=3;

No need to initialize a and b here

int main()

int main()

int sum;

type

int sum;

sum = add(5,4);

sum = add(5,4);

Here we call the add function

Then we pass the parameters as 5 and 4

5 will be stored in a and 4 will be stored in b

The returned value c will be stored in sum

Hence type here

printf(“Sum is %d\n”,sum);

return 0;

A non-void function must use a return statement that returns a value.

Come back to our terminal

gcc function.c -o fun

Type

./fun

gcc function.c -o fun

let us execute

./fun

Output

The result is 9

Come back to our program

Let me change a few things here

Click on save as option

Type

cpp

Click on Save as option

Save the file with .cpp extension

<iostream>

<iostream>

using namespace std;

So there is no need to change anything here

cout<<

as we use cout<< function to print a line in C++

So delete it

<<sum <<”\n”

Then type sum two opening angle brackets again

and within the double quotes backslash n

Delete this closing bracket

Click on save

Come back to the terminal

g++ function.cpp -o fun1

Type

./fun1

g++ function.cpp -o fun1

Here we have fun1, this is because we don't want to overwrite the output file.

press Enter

To execute

Type

./fun1

Output

The result is 9.

Type

x

Suppose here we type x in the place of 4.

I will retain the rest of the code as it is.

and compile the program

error

x undeclared

This is because x is a character variable

And our add function has integer variable as an argument

So there is a mismatch in return type and return value.

Let us fix the error

4

Let us execute this program

Yes! it is working

Delete

4

Suppose here we pass only 1 parameter

Let us delete 4

Switch to the terminal

Error

too few arguments to function 'add'

int a and int b

And here we are passing only one parameter

Hence it is giving an error

Type 4 here

Click on Save

Switch back to the terminal

Now let go through a quick summary

Come back to our slides

Function without arguments

Function with arguements

Significance of a return statement

Assignment

Write a program to calculate the square of a number using function.

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