Linking header file still leads to undefined reference

I have three files: vector2d.h referencing my functions. vector2d.c defining my functions. test_vectors.c as the main file.

test_vectors.c doesn't build because it returns an undefined reference error for every function.

I'm using geany and I don't necessarily have a terminal to write anything in, just a build and run button.

vector2d header

typedef struct {
    double x;
    double y;
} vec2d;

void display_vector(const vec2d v);
double magnitude(const vec2d v);
vec2d add(const vec2d v1, const vec2d v2);
vec2d scale(const vec2d v, const double factor);
double dot_product(const vec2d v1, const vec2d v2);

vector2d C file

#include "vector2d.h"
#include <stdio.h>
#include <math.h>

void display_vector(const vec2d v){
    printf("%.2f, %0.2f", v.x, v.y);
}

double magnitude(const vec2d v){
    double result = sqrt((v.x*v.x) + (v.y * v.y));
    return result;
}

vec2d add(const vec2d v1, const vec2d v2){
    vec2d result;
    result.x = v1.x + v2.x;
    result.y = v1.y + v2.y;
    return result;
}

vec2d scale(const vec2d v, const double factor){
    vec2d result;
    result.x = v.x * factor;
    result.y = v.y * factor;
    return result;
}

double dot_product(const vec2d v1, const vec2d v2){
    double result = (v1.x * v2.x) + (v1.y * v2.y);
    return result;
}

test_vectors file

#include <stdio.h>
#include "vector2d.h"


int main (void){
    int choice;
    vec2d v1, v2, result;
    double factor, dot;
    
    do {
        printf("1) Add vectors; 2) Scale vector; 3) Dot product; 4) Exit: ");
        scanf("%d", &choice);
        
        switch(choice){
            case 1:
                printf("Enter vector 1 (x, y): ");
                scanf("(%lf, %lf)", &v1.x, &v1.y);
                printf("\n");
                
                printf("Enter vector 2 (x, y): ");
                scanf("(%lf, %lf)", &v1.x, &v1.y);
                printf("\n");
                
                result = add(v1, v2);
                
                printf("Result: ");
                display_vector(result);
                printf("\n");
                
            case 2:
                printf("Enter vector (x, y): ");
                scanf("(%lf, %lf)", &v1.x, &v1.y);
                printf("\n");
                
                printf("Enter scaling factor: ");
                scanf("%lf", &factor);
                printf("\n");
                
                result = scale(v1, factor);
                
                printf("Result: ");
                display_vector(result);
                printf("\n");
                
            case 3:
                printf("Enter vector 1 (x, y): ");
                scanf("(%lf, %lf)", &v1.x, &v1.y);
                printf("\n");
                
                printf("Enter vector 2 (x, y): ");
                scanf("(%lf, %lf)", &v1.x, &v1.y);
                printf("\n");
                
                dot = dot_product(v1, v2);
                
                printf("Result: %f\n", dot);
                
            case 4:
                printf("Bye!");
                break;  
        }
        
    } while(1);
    
    return 0;
}

I've tried putting the function prototypes in test_vectors.c, but that obviously didn't help. I can't seem to link them properly using this geany IDE.