Tuesday, May 06, 2014

Sum of Digits of a number Function (Recursive and Non Recursive) - C Program

Problem Question


A 5-digit positive integer is entered through the keyboard, write a function to calculate sum of digits of the 5-digit number:
(1) Without using recursion
(2) Using recursion

Explanation of Problem


We wish that the user enters a 5 digit number. We have to make 2 functions one of which will calculate the sum of digits normally, and other will use recursion to do the same.

Code


#include <stdio.h>

/**@Title: SumOfDigitsFunctions.c*
*@Language: ANSI C*
*@Compiler: GNU GCC*
*@IDE: Code::Blocks 13.12*
*@Author: Toxifier*
*@URL: http://letsplaycoding.blogspot.com/*
*@Date: 06-05-2014*
*/

int digSum(int number)
{
  int sum = 0;
  while (number)
  {
    sum += number % 10;
    number /= 10;
  }
  return sum;
}

int digSumRec(int number)
{
  if (number)
    return (number % 10 + digSumRec(number / 10));
  else
    return 0;
}

int main()
{
  int number, sum = 0;
  printf("\n\nEnter a 5 digit number: ");
  scanf("%d", &number);
  printf("\nSum without recursion: %d\nSum with recursion: %d\n\n", digSum(number), digSumRec(number));
  system("pause");
  return 0;
}

Explanation of Code


#include <stdio.h> -> This is the step which occurs before compilation starts. The compiler calls the C Preprocessor to include the STDIO(Standard Input Output) header file into the program, thus letting the use of the standard input/output functions like printf() and scanf() which come from STDIO.H

int main() -> The entry point of the program where the execution starts. This function has to be named main. As per the ANSI specification, the return type has to be int. If you use the traditional C, you may use void as the return type. Since the return type is specified as int in my program, I have to use a return statement at the end of my code. So I use return 0 since zero returned from a function, by convention, implies a correct execution of the program. The return values are used to debug the program.

printf() -> This is a standard output function used to print something on the screen. We have to pass a string to this function which will be displayed on user's terminal.

scanf() -> This is the scanf() function which waits for the user to enter certain value using his/her keyboard. We store the user input at the location in memory which is pointed to by the variable whose address is passed to this function.

int digSum(int number)
{
int sum = 0;
while (number)
{
sum += number % 10;
number /= 10;
}
return sum;
}


This is the first function that calculates the sum of digits normally. main() calls this functions with the user entered number as the argument. Inside the function, I have devised a while loop. Why have I used 'number' in the condition? Since I will extract the last digit and add it to the running sum into the variable 'sum', and also divide the number by 10 in each iteration. Once the number turns to be 0 on continuous dividing, the control comes out of the loop, and 'sum' is returned.

int digSumRec(int number)
{
if (number)
return (number % 10 + digSumRec(number / 10));
else
return 0;
}


This is our recursive function. In this case, we do the same thing as above, but instead of while loop, we achieve the same thing using recursion. The if condition is similar to the while loop block in the former function. The statement which executes when the 'if' block condition is true, calls the function digSumRec recursively, but the argument is passed as number / 10 instead of number. Thus as soon as number / 10 returns zero, the if block is not executed. Moreover, the return statement in the if block does the addition part. It extracts the last digit from the 'number' and adds to it what is returned by the recursive call to the procedure.

system("pause") -> This statement is used to pause the program, until user presses a key. This function is not necessary in your program, I use it to see my outputs paused. If you use cmd to run your programs, you might not need this. If you use linux/unix you might not need this. Depending on your compiler, this function may or may not work. Moreover, removing this line of code from this program, doesn't affect the functionality of the program.

Output(s)



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