Heyy, what's up?

I need some help doing this (it's an assingment, by the way)...

This is my code:

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

void main(void){
    int d, m, y, o; //day, month year, option
    int c,g,k,i,j,l; //variables needed to calculate the date..
tryagain:
    printf("Write a year to calculate it's easter date:  ", a);
    scanf("%d", &a);

    if (a < 1000 || a > 9999){
            printf("That year is not valid.\n");
            printf("Try again (0 = no/1 = yes): ", o);
            scanf("%d", &o);
            if (o == 1) {
                    system("CLS");
                    goto tryagain;
            }
            else {
                printf("Bye Bye...\n");
            }
    }
    else if(a>=1000 && a < 10000){
            //Calculation of the easter date...
            c = y/100;
            g = y % 19;
            k = (c - 17)/25;
            i = (c - c/4 - (c - k)/3 + 19*g + 15) % 30;
            i = i - (i/28)*(1 - (i/28)*(29/(i + 1))*((21 - g)/11));
            j = (c + c/4 + i + 2 - c + c/4) % 7;
            l = i - j;
            m = 3 + (l + 40)/44;
            d = l + 28 - 31*(m/4);

            m = 3+(l+40)/44;
            d=m+28-31*(m/4);
            printf("\n==================================\n");
            printf("La fecha del Easter es: %d/%d/%d.\n", d, m, c);
            printf("==================================\n\n");
    }
    printf("Go again (0 = no/1 = yes): ", o);
    scanf("%d", &o);
    if (o == 1) {
        system("CLS");
        goto tryagain;
        }
    else {
        printf("Bye...\n");
        }
    system("PAUSE");
    return 0;
}
The code prints the same dates... This is based on Oudin's algorithm.

Thanks in advance!