Thread: Function Addiding Two Integers Returns Incorrect Result

Hello Everyone:

I am new to functions. I would like to add two numbers input by the user. Though the math output generated in the main function works fine, "add_nums" outputs a ten digit value for something as basic as 2 + 3. I would appreciate your thoughts.

Code:

#include <stdio.h>

 /* Function Prototype */
 /*----------------------*/
 int add_nums (int x, int y);

 int main (void) /* begin function main */
{
  /* Variable Declarations */
  /*-----------------------*/
  
  int num_1, num_2; 
 
  /* Greeting and objective */
  /*------------------------*/
  printf ("\n This program adds numbers using a function. \n\n");

  printf ("\n Please enter an integer: "); /* prompt user*/
  scanf ("%i", &num_1); /* store 1st number */
  fflush (stdin); /* clearing buffer */
  printf ("\n Enter the second integer: "); /* prompt user */
  scanf ("%i", &num_2); /* store 2nd number */
  fflush (stdin); /* clearing buffer */
  printf ("\n Adding in main you get %i.", num_1 + num_2);
  printf ("\n Adding via function you get %i.", add_nums(num_1, num_2));

  printf ("\n Thanks for using the program.\n\n"); /* pgm end */

  getchar(); /* wait for character. */

  return 0;
}/* end function main */

/* Function(s) */
/*-------------*/
int add_nums (int x, int y)
 {
  int a, b, sum;
  sum = a + b;
  return sum;
 } /* end add_nums */

In your "add_nums()" function, variables "a" and "b" are uninitialized, so you're adding two garbage values and returning that sum.

It looks like you want to use "x" and "y" instead (that is how you access the values passed to the function from the caller).

Also, using "fflush()" on stdin is technically undefined behavior: FAQ > Why fflush(stdin) is wrong - Cprogramming.com

Thank you Matticus!

I resorted to using variables a and b to get past CFree's "declaration of 'x' shadows a parameter" warning.

Though the function add_nums has been modified, the result is incorrect. Maybe I misunderstood your suggestion? Here're the changes...

Code:

int add_nums (int x, int y)
{
 int x, y, sum;
 sum = x + y;
 return sum;

"x" and "y" are already declared in the parameter list, so you do not need to re-declare them as you're doing on line 3 of the sample you posted.

That's it! You're awesome Matticus!
Thank you for your input...much appreciated. The following works perfectly...

Code:

int add_nums (int x, int y)
{
 int sum;
 sum = x + y;
 return sum;
} /* end add_nums */

Try this please

Originally Posted by nul

Code:

#include <stdio.h>
 
 /* Function Prototype */
 /*----------------------*/
 int add_nums (int x, int y);
 
 int main (void) /* begin function main */
{
  /* Variable Declarations */
  /*-----------------------*/
   
  int num_1, num_2; 
  
  /* Greeting and objective */
  /*------------------------*/
  printf ("\n This program adds numbers using a function. \n\n");
 
  printf ("\n Please enter an integer: "); /* prompt user*/
  scanf ("%i", &num_1); /* store 1st number */

  printf ("\n Enter the second integer: "); /* prompt user */
  scanf ("%i", &num_2); /* store 2nd number */

  printf ("\n Adding in main you get %i.", num_1 + num_2);
  printf ("\n Adding via function you get %i.", add_nums(num_1, num_2));
 
  printf ("\n Thanks for using the program.\n\n"); /* pgm end */
 
  getchar(); /* wait for character. */
 
  return 0;
}/* end function main */
 
/* Function(s) */
/*-------------*/
int add_nums (int x, int y)
 {
  return (x+y);
 } /* end add_nums */