if((y>1900) && (y % 4 == 0) && (m < 2))
{
    year--;
    day = year % 7;
    switch(day)
    {
        case 0:
            printf("day is sat\n");
            break;

        case 1:
        printf("day is sun\n");
        break;

        case 2:
            printf("day is mon\n");
            break;

        case 3:
            printf("day is tue\n");
            break;

        case 4:
            printf("day is wen\n");
            break;

        case 5:
            printf("day is thur\n");
            break;

        case 6:
            printf("day is fri\n");
            break;

        case 7:
            printf("day is sat\n");
            break;
    }
}