A C program to reverse the given string using recursion

By | October 2, 2013

Explanation of FUNCTION:

A function is a block of code that has a name and it has a property that it is reusable i.e. it can be executed from as many different points in a C Program as required.

Function groups a number of program statements into a unit and gives it a name. This unit can be invoked from other parts of a program. A computer program cannot handle all the tasks by itself. Instead its requests other program like entities – called functions in C – to get its tasks done. A function is a self contained block of statements that perform a coherent task of same kind.

The name of the function is unique in a C Program and is Global. It means that a function can be accessed from any location within a C Program. We pass information to the function called arguments specified when the function is called. And the function either returns some value to the point it was called from or returns nothing.

We can divide a long C program into small blocks which can perform a certain task. A function is a self contained block of statements that perform a coherent task of same kind.

 

Recursive function is a function which calls itself. Calling a function within itself makes it a endless loop. So we need to take care that there must be a termination condition in every recursive function.

For writing a function and using it in the C program, we should declare the function in the MAIN function. Declaration has to done in the area before the code starts, same area where we declare data variables.

void reverse_rec(char *STR);

Function returns value and the ones which does not return any value is called and declared as void. This function which we are writing returns the gcd in decimal form as output. The values inside the round brackets are called Arguments. The Argument and return type are integer type. A function can return only one value so we have to take only one data type in which its value is expected.

Let’s identify variables needed for this program.
First variables will be the one which will save the value entered by the user S[50]. The identified variables are S[50].

Now, Selection of data type is char array data type due to the values expected are string and they will be holding value as char array data type.

Main program needs only declaration of variables and function prototype. Also messages for user and scanning string  S[50] print the message and call the Reverse FUNCTION which will print the characters within the function call itself. Their is no single value to be returned hence the return value will be void.

#include<stdio.h>
void main()
{
 void reverse_rec(char*);
 int S[50];
 printf("\nENTER STRING TO REVERSE : ");
 scanf("%s",&S);
 printf("\nREVERSED STRING IS :- ");
 reverse_rec(S);
 getch();
}

Let’s identify variables needed for function which is part of program outside main function.
their are no variable of the function.

In this program there is a risk of generating an ENDLESS LOOP. Here we have to Check the TERMINATION condition is given or not. If condition will have character pointer will be true till the character is present and when the character is NULL it will change to false. In beginning print a character will print the straight order and to print reverse order we have to print it after function call.

void reverse_rec(char *STR)
{
     if(*STR)
     {
      reverse_rec(STR+1);
      printf("%c",*STR);
     }
}

Note:- Remember whenever you are calling a function which is returning a value it should always be assigned to a variable of same data type or called inside the printf function as variable.

C program code :

  1. #include<stdio.h>
  2. void main()
  3. {
  4.  void reverse_rec(char*);
  5.  int S[50];
  6.  printf("\nENTER STRING TO REVERSE : ");
  7.  scanf("%s",&S);
  8.  printf("\nREVERSED STRING IS :- ");
  9.  reverse_rec(S);
  10.  getch();
  11. }
  12. void reverse_rec(char *STR)
  13. {
  14.      if(*STR)
  15.      {
  16.       reverse_rec(STR+1);
  17.       printf("%c",*STR);
  18.      }
  19. }

Screen Shots :-

C_program_Reverse_Recursion

C_program_Reverse_Recursion_Output

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