Nick Heiner - 1 year ago 101

C Question

I'm trying to learn C by writing a simple program to output Fibonacci numbers. It isn't working.

**fibonacci.h**

`unsigned int fibonacci_recursive(unsigned int n);`

`#include <stdio.h>`

#include "fibonacci.h"

main() {

unsigned int i;

for (i = 0; i < 10; i++) {

printf("%d\t%n", fibonacci_recursive(i));

}

getchar();

}

`unsigned int fib_rec(unsigned int n);`

main(unsigned int n) {

return fib_rec(n);

}

unsigned int fib_rec(unsigned int n) {

if (n == 0) {

return 0;

}

if (n == 1) {

return 1;

}

return fib_rec(n - 1) + fib_rec(n - 2);

}

This is the error message VS 2010 gives me when I try to build the project:

`1>ClCompile:`

1> fibonacci_recursive.c

1>fibonacci_recursive.obj : error LNK2005: _main already defined in fibonacci.obj

1>fibonacci.obj : error LNK2019: unresolved external symbol _fibonacci_recursive referenced in function _main

1>c:\users\odp\documents\visual studio 2010\Projects\Fibonacci\Debug\Fibonacci.exe : fatal error LNK1120: 1 unresolved externals

1>

1>Build FAILED.

1>

What am I doing wrong here? Thanks for helping someone new to C.

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Answer Source

Your approach seems strange, you should have:

- a main file (example
`main.c`

) with the main method and that includes`fibonacci.h`

- a
`fibonacci.h`

with the prototype`unsigned int fibonacci_recursive(unsigned int n);`

- a
`fibonacci.c`

with the implementation of the method, and it should include`fibonacci.h`

too

Actually you define `main`

function twice too..

**main.c**

```
#include <stdio.h>
#include "fibonacci.h"
main()
{
unsigned int i;
for (i = 0; i < 10; i++)
{
printf("%d\t%n", fibonacci_recursive(i));
}
getchar();
}
```

**fibonacci.h**

```
unsigned int fibonacci_recursive(unsigned int n);
```

**fibonacci.c**

```
#include "fibonacci.h"
unsigned int fibonacci_recursive(unsigned int n)
{
if (n == 0)
{
return 0;
}
if (n == 1) {
return 1;
}
return fibonacci_recursive(n - 1) + fibonacci_recursive(n - 2);
}
```

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