First time programmer need a little help

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1. First time programmer need a little help

So I am pretty new to programming as I am a freshman in college. I have written out my program for the assignment this week and I just can't for the life of me figure out how to get rid of theses errors.

Code:
```#include <stdio.h>

void greet_user(void);
double get_initial_cost(void);
double get_fuel(void);
double get_tax(void);
double calculate_cost(double initial, double fuel, double tax)
void give_results(double calculate)

int main (void)
{
greet_user();
get_initial_cost();
get_fuel();
get_tax();
calculate_cost();
give_results();
return (0);
}

void greet_user(void)
{
printf("This program will calculate the cost of your house after");
printf(" owning it for 5 years.");
return;
}

double get_initial_cost(void)
{
double initial;
scanf("%lf", &initial);
return(initial);
}

double get_fuel(void)
{
double fuel;
scanf("%lf", &fuel);
return(fuel);
}

double get_tax(void)
{
double tax;
scanf("%lf", &tax);
return(tax);
}

double calculate_cost(double initial, double fuel, double tax)
{
double cost;
cost = (initial + fuel + tax) * 5.0;
return(cost);
}

void give_results(double cost)
{
printf("The total cost of your house after owning it for");
printf(" five years is %f",cost);
return;
}```
I get these errors:

In function 'calculate_cost':
10: error: parse error before "int"
13: error: old-style parameter declarations in prototyped function definition
at top level:
54: error: redefinition of 'calculate_cost'
13: error: previous definition of 'calculate_cost' was here

I know these are some dumb errors, but I have been trying to get rid of them for the past couple of hours and nothing seems to work.

Any help is greatly appreciated!

2. Did you try adding ; to the end of lines 7 and 8? The other errors you are having probably cascade from this.