Linker Error/Undefined Reference

[liljp617]

I know there's a million of these but I've been trying to work through it for a while and can't grasp it.

Basically have to make a calculator using functions for the basic mathematical operations.

Here's a small bit of my code, and I'm getting the same error for each of my switch statements so one answer should work for all.

#include <stdio.h>
#include <stdlib.h>

     int add(int, int); //addition function prototype
     int subtract(int, int); //subtraction function prototype
     int multiply(int, int); //multiply function prototype
     int divide(int, int); //divide function prototype
     int modulus(int, int); //modulus function prototype
     int primeNumber(int); //test prime function prototype
     int power(int, int); //exponent function prototype
     int factorial(int); //factorial function prototype

int main()
{
      
      /*Declare/Initialize Variables*/
     int iSelection = 0; //Menu selection
     int iFirstDigit = 0;  //First digit entered
     int iSecondDigit = 0; //Second digit entered
     
while (iSelection !=10)
{
     
     /*Begin Calculator*/
     printf("\n                Calculator\n\n");
     
     printf("1   Addition\n");
     printf("2   Subtraction\n");
     printf("3   Multiplication\n");
     printf("4   Division\n");
     printf("5   Modulus (Integers Only)\n");
     printf("6   Test If Prime (Integers Only)\n");
     printf("7   Factorial (Integers Only)\n");
     printf("8   Power\n");
     printf("10  Exit Calculator\n");
     
     /*Prompt User To Begin Interaction*/
     printf("\nPlease select one of the options (1-7): ");
     scanf("&#37;d", &iSelection);


     switch(iSelection) //begin switch
     {
          case 1:
                 printf("\nPlease enter first digit to be added: ");
                 scanf("%d", &iFirstDigit);
                 printf("\nPlease enter second digit to be added: ");
                 scanf("%d", &iSecondDigit);
                 printf("\nThe sum of the two numbers is %d\n\n", add(iFirstDigit, iSecondDigit));
     
          int add (int iFirstDigit, int iSecondDigit)
               {
                  return iFirstDigit + iSecondDigit;
               }
               break; //end case 1

My compile error is

[Linker error]: undefined reference to 'add'



I'm assuming it has something to do with how I've defined/prototyped my function or something along those lines, but I can't spot the error myself.

I've looked through past threads of this nature and couldn't really find the solution. Any help at all is appreciated.

[nonoob]

Yes, you have to write those functions add(), subtract(), etc. I think you've started doing that with the add() function - but it's embedded inside the case statement. You need to move that code outside of the main(). At the top I would put them. Then they act as prototypes and you don't have a need for the prototype statements. Or you can place the functions AFTER the main. Then you DO need the prototype statements.

int add (int iFirstDigit, int iSecondDigit)
               {
                  return iFirstDigit + iSecondDigit;
               }

int subtract...

int main()
{
      
 ...

[liljp617]

Thank you thank you

So simple -.-