C Programming

A function in C language is declared as follows,

return_type function_name(formal parameter list)
{
       Function_Body;
}

A pointer holding the reference of the function is called a pointer to a function. In general, it is declared as follows.

T (*fun_ptr) (T1,T2…); Where T is any date type.

Once fun_ptr refers to a function the same can be invoked using the pointer as follows.

fun_ptr();
[Or]
(*fun_ptr)();

By default, the functions are called by value.

Yes, any user-defined function can call any function.

A function’s definition prefixed with a static keyword is called a static function. You would make a function static if it should be called only within the same source code.

When a function calls itself, and this process is known as recursion. The function that calls itself is known as a recursive function.

Recursive function comes in two phases:

• Winding phase
• Unwinding phase

Winding phase: When the recursive function calls itself, and this phase ends when the condition is reached.

Unwinding phase: The unwinding phase starts when the condition is reached, and the control returns to the original call.

Example of recursion

#include   
int calculate_fact(int);  
int main()  
{  
 int n=5,f;  
 f=calculate_fact(n); // calling a function  
 printf("factorial of a number is %d",f);  
  return 0;  
}  
int calculate_fact(int a)  
{  
  if(a==1)  
  {  
      return 1;  
  }  
  else  
  return a*calculate_fact(a-1); //calling a function recursively.  
}  

Output: factorial of a number is 120

Call by value: We send only values to the function as parameters. We choose this if we do not want the actual parameters to be modified with formal parameters but just used.

Call by reference: We send the address of the actual parameters instead of values. We choose this if we do want the actual parameters to be modified with formal parameters.

The parameters sent to the function at calling end are called as actual parameters while at the receiving of the function definition called formal parameters.

Example of Call by Value method

#include  
void change(int,int);  
int main()  
{  
    int a=25,b=50;  
    change(a,b); 
    printf("The value assigned to a is: %d",a);  
    printf("n");  
    printf("The value assigned to of b is: %d",b);  
    return 0;  
}  
void change(int x,int y)  
{  
    x=100;  
    y=200;  
}

Example of Call by Reference method

#include
void change(int*,int*);  
int main()  
{  
    int a=25,b=50;  
    change(&a,&b); 
    printf("The value assigned to a is: %d",a);  
    printf("n");  
    printf("The value assigned to b is: %d",b);  
    return 0;  
}  
void change(int *x,int *y)  
{  
    *x=100;  
    *y=200;  
}

Both the functions are designed to read characters from the keyboard and the only difference is that

getch(): reads characters from the keyboard but it does not use any buffers. Hence, data is not displayed on the screen.

getche(): reads characters from the keyboard and it uses a buffer. Hence, data is displayed on the screen.

Example:

#include
#include
int main()
{
     char ch;
     printf("Please enter a character ");
     ch=getch();
     printf("nYour entered character is %c",ch);
     printf("nPlease enter another character ");
     ch=getche();
     printf("nYour new character is %c",ch);
     return 0;
}

Output:

Please enter a character
Your entered character is x
Please enter another character z
Your new character is z