[1] Leap Year Test

int isleapyear=0, yy;

if (yy%400==0 || (yy%4==0 && yy%100!=0))
	isleapyear=1;


[2] ID# check

int valid;
char idno[9]="A1234567";
gets(idno);

valid=0;

if (strlen(idno)==8){
	valid=1;

	if (idno[0]<'A' || idno[0]>'Z') valid=0;

	for (i=1; i<7; i++)
		if (idno[i]<'0' || idno[i]>'9') valid=0;

	if ( ! (idno[7]=='A' ||
		(idno[7]>='0' && idno[7]<='9')) ) valid=0;
}


[3] DOB check

char date[11]="25/12/2008", s[5];
int dd,mm,yy;
gets(date);

strncpy(s,date+0,2);	dd=atoi(s);
strncpy(s,date+3,2);	mm=atoi(s);
strncpy(s,date+6,4);	yy=atoi(s);

ok = (dd>=1 && dd<=31 && mm>=1 && mm<=12 && yy>1900);