C - Functions

 
What is Function?

1. An activity that is natural to or the purpose of a person or thing. "bridges perform the function of providing access across water"
2. A relation or expression involving one or more variables. "the function (bx + c)"

• In programming languages it can be something which performs a specific service or a task
• Generally a function has 3 properties

– Takes Input

– Perform Operation

– Generate Output

Writing a Function..
Syntax:
return_data_type function_name(arg_1, arg_2, ..., arg_n)
{
/* Function Body */
}
Example:
int function(int arg_1, int arg_2)
{
/* Function Body */     
}

How to Call a Function:
#include <stdio.h>
int main()
{
int x, y;
x = 2;
y = foo(x);    //The Fucntion get's Called here..
printf(“y is %d\n”, y);
return 0;
}

int foo(int x)
{
int ret = 0;
ret = x + 1;
return ret;
}

Advantages of using Function:

• Re usability

1. Functions can be stored in library & re-used
2. When some specific code is to be used more than once, at different places, functions avoids repetition of the code.

• Divide & Conquer

1. A big & difficult problem can be divided into smaller sub-problems and solved using divide & conquer technique

• Modularity can be achieved.
• Code can be easily understandable & modifiable.
• Functions are easy to debug & test.
• One can suppress, how the task is done inside the function, which is called Abstraction

Detailed look of function:

#include <stdio.h>
int main()   // The main function
{
int num1 = 10, num2 = 20;
int sum = 0;
sum = add_numbers(num1, num2);  //The function call
printf(“Sum is %d\n”, sum);
return 0;
}

int add_numbers(int num1, int num2)   //'int' is a Return type
{
int sum = 0;
sum = num1 + num2;  // Function
return sum;   // Return from function
}

Function & Stack

Functions – Parameter Passing Types:

• Difference between Pass by Value & Pass by reference

Pass by Value:

• This method copies the actual value of an argument into the formal parameter of the function.
• In this case, changes made to the parameter inside the function have no effect on the actual argument.

Pass by Reference:

• This method copies the address of an argument into the formal parameter.
• Inside the function, the address is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument.

Example for Pass by Value:
#include <stdio.h>
int add_numbers(int num1, int num2);
int main()
{
int num1 = 10, num2 = 20, sum;
sum = add_numbers(num1, num2);
printf(“Sum is %d\n”, sum);
return 0;
}

int add_numbers(int num1, int num2)
{
int sum = 0;
sum = num1 + num2;
return sum;
}
Example for Pass by Value:
#include <stdio.h>
void modify(int *num_ptr)
{
*num_ptr = *num_ptr + 1;
}

int main()
{
int num = 10;
printf(“Before Modification\n”);
printf(“num1 is %d\n”, num);
modify(&num);
printf(“After Modification\n”);
printf(“num1 is %d\n”, num);
return 0;
}
Working - Pass by Value : 

Working - Pass by Reference : 

Advantages of Pass by Reference :

• Return more than one value from a function
• Copy of the argument is not made, making it fast, even when used with large variables like arrays etc.
• Saving stack space if argument variables are larger (example – user defined data types)

Passing Array in Function

#include <stdio.h>
void print_array( int array[] );
int main()
{
int array[5] = {10, 20, 30, 40, 50};
print_array(array);
return 0;
}

void print_array(int *array[])
{
int iter;
for (iter = 0; iter < 5; iter++)
{
printf(“Index %d has Element %d\n”, iter, array[iter]);
}
}

Functions – return type

• Local return
• Void return

.