code won't compile, can't see the error, help troubleshooting

[cameuth]

My compiler tells me I have an error in line 100 with an output error in daysinmonth. This doesn't make sense to me as I wasn't messing with that function at the time it came out as an error. heres the code, is there something I'm missing? At first it told me the variable i was not initialized, so I made the variable global and that gave me this new error...

#include <stdio.h>
#include <time.h>
int days, month, year, days_1, month_1, year_1, leapy=0, ndays, ddays, days_total=0, days_beforeleap, days_years, i;

int daysinmonth(int month)
{
        switch(month)
        {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12:
                return 31;
        case 2:
                return 28;
        case 4:
        case 6:
        case 9:
        case 11:
                return 30;
        default:
                return -1;
        }
int is_leap_year(int year)
{
        while(year<year_1)
        {
                if(year%400 ==0 || (year%100 != 0 && year%4 == 0))
                {
                ++leapy;
                ++year;
                }
                else
                {

                ++year;
                }
        }

}
int daystoyears(int year,int year_1)
{
int total_years;
total_years=year_1-year;
days_years=total_years*365;
return days_years;
}
int daysinyear(int days, int month, int days_1, int month_1)
{
int i;
for(i = month;i < month_1;++i)
days_total += daysinmonth(i);

days_total+=days_1;
days_total=days_total-1;
return days_total;
}

int main(void)
{
char a, b, a1, b1;
printf("intput a date in the follwing format:\n");
printf("mmddyyyy: in other words the two digit day,two digit month,\n");
printf("and four digit year, with no slashes or heifens anywhere.\n");
scanf("%d%c%d%c%d", &month, &a, &days, &b, &year);
printf("enter the later date in the same format:\n");
scanf("%d%c%d%c%d", &month_1, &a1, &days_1, &b1, &year_1);
        if(month<0 || month>12 || days<0 || days>31 || year<0)
        {
        printf("data not valid\n");
        exit(1);
        }

        if(year>year_1)
        {
        printf("data not valid\n");
        exit(1);
        }
        if(year==year_1 && month>month_1)
        {
        printf("data not valid\n");
        exit(1);
        }
        if(year==year_1 && month==month_1 && days>days_1)
        {
        printf("data not valid\n");
        exit(1);
        }
daysinyear(days, month, days_1, month_1);
printf("total days=%d\n",days_total);
daystoyears(year, year_1);
printf("total days=%d\n",days_years);
return 0;
}