Please check this coding for me!

I was asked to write a simple billing system. So this is the code i can come up with. I know there are some mistakes there but i can't figure what is it. Please, check it for me and correct it.

Code:

/*Updating a Series of Customer Accounts(simplified billing system)*/

#include <stdio.h>

void readinput(int i)
void writeoutput(int i)

struct date{
	int month;
	int day;
	int year;
};


struct account
{
	char name[40];
	char street[40];
	char city[40];
	int acct_no;
    float previous_balance;
	float current_payment;
	float new_balance;
    struct date lastpayment;	
}
customer[100];

main()

{
	int i,n;

	printf("CUSTOMER BILLING SYSTEM\n\n");
	printf("How many customer are there?");
	scanf("%d",&n);


	{
		readinput(i);

		customer[i].new_balance=customer[i].previous_balance-customer[i]current_payment;
	}
	
	

   
	




	

		writeoutput(i);
}

void readinput(int i)

{

	printf("Customer no.%d\n",i+1);
	
	printf("   Name:");
    scanf("%[^\n]",customer[i].name);

	printf("   Street:");
    scanf("%[^\n]",customer[i].street);

	printf("   City:");
    scanf("%[^\n]",customer[i].city);

	printf("   Account number:");
	scanf("%d",&customer[i].acct_no);

	printf("   Current payment:");
	scanf("%f",&customer[i].currentpayment);

	printf("   Payment date (mm/dd/yyyy):");
	scanf("%d%d%d",&customer[i].month,
		           &customer[i].day,
				   

	return;

}		

void writeoutput(int i);

{
	printf("\nName:   %s",customer[i].name);

	printf("   Account number:%d\n",customer[i].acct_no);

	printf("Street:   %s\n",customer[i].street);

	printf("City   %s\n\n",customer[i].city);

	printf("Previous Balance: %7.2f",customer[i].previousbalance);

	printf("   Current Payment: %7.2f", customer[i].currentpayment);

	printf("   New balance: %7.2f\n\n",customer[i].newbalance);

    return;
	
}

And what are the symptoms of these mistakes?

Do you go to your doctor saying "I don't feel well" and expect the doctor to immediately know that it's your foot that hurts?

--
Mats

A development process
Step 1 is don't write more code than you're prepared to deal with being wrong when you try to compile it.

Writing 10 lines, compile and fix 1 error - good.
Writing 100 lines, compile and getting lots of errors - bad. Especially if you then dump the whole sorry mess on a message board for someone else to fix.

I might care if it was nicely indented and made good use of blank lines to separate different areas of the code, but it doesn't even manage to do that.