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

• What is a function

• Syntax of a function

• Significance of return statement

We will do this through examples.

We will also see some common errors and their solutions.

• Ubuntu Operating system version 11.10
• gcc and g++ Compiler version 4.6.1

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

Every program consists of one or more functions.

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

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 open it.

function.c

And I have saved the file with the extentsion .c

Let me explain the code.

#include <stdio.h>

void add()

Here we have defined 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 and

• 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 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.

Type int main()

Type 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.

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

Let us execute.

Output

Sum is 9

Come back to our program.

Let me change a few things here.

function.cpp in Name field >> Click on "Save"

Now save the file with .cpp extension.

Click on Save.

<iostream>

<iostream>

using namespace std;

So there is no need to change anything here.

cout<<

Delete the comma.

<<sum <<”\n”

After sum , again type two opening angle brackets.

Within double quotes, type 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 fun.

Press Enter.

Type

./fun1

Output

Sum 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.

error

x was not declared in this scope.

This is because x is a character variable. It was not declared anywhere.

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.

Let us execute again.

Yes! it is working.

Delete

4

Suppose here we pass only one parameter.

Delete 4.

Error

too few arguments to function 'int add (int, int)'

int a and int b.

And here we are passing only one parameter.

Hence it is giving an error.

Type 4.

Click on Save .

Switch back to the terminal.

Come back to our slides.

• Function
• Syntax of function
• Function without arguments
  • Eg- void add()
• Function with arguments
  • Eg- int add(int a, int b)

Assignment

Write a program to calculate the square of a number.

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