Write a menu based program which allows users to perform the following tasks : 1. Calculate the sum of digits of a number 2. Reverse a number 3. Determine whether a year is leap or not. 4. Display the multiplication table of a number upto 10 5. Calculate Xn 6. Calculate n! 7. Determine whether a date entered is valid or not. The program should exit only when the user desires.

#include <stdio.h>

int main(void)
{
int choice, year;
long int num;

do
{
printf("\n1.Sum of digits\n2.Reverse a number\n3.Leap\n4.Multiplication table\n\
5.Power\n6.Factorial\n7.Valid date\n8.Exit\nChoice :");
scanf("%d", &choice);

switch(choice)
{
case 1:
{
int sum = 0;
printf("\nEnter a number :");
scanf("%ld", &num);
while(num > 0)
{
sum = sum + (num % 10);
num /= 10;
}
printf("\nSum of digits is %d", sum);
break;
}
case 2:
{
long int rev = 0;
printf("\nEnter a number :");
scanf("%ld", &num);
while(num > 0)
{
rev = (rev * 10) + (num % 10);
num /= 10;
}
printf("\nReverse is %ld", rev);
break;
}
case 3:
{
printf("\nEnter a year :");
scanf("%d", &year);
if((year % 100 == 0 && year % 400 == 0) ||
(year % 100 != 0 && year % 4 == 0))
printf("\n%d is a leap year", year);
else
printf("\n%d is NOT a leap year", year);
break;
}
case 4:
{
int cnt;
printf("\nEnter a number :");
scanf("%ld", &num);
for(cnt = 1 ; cnt <= 10 ; cnt++)
{
printf("\n%ld X %d = %ld", num, cnt, num * cnt);
}
break;
}
case 5:
{
int base, index, tmp;
float res = 1.0;
printf("\nEnter the base and index :");
scanf("%d%d",&base, &index);
tmp = index;
for( ; index != 0 ; )
{
res *= base;
if(index > 0) index--;
else index++;
}
if(tmp < 0)
res = 1 / res;
printf("\n%d raised to %d is %f", base, tmp, res);
break;
}
case 6:
{
long int fact;
printf("\nEnter a number :");
scanf("%ld", &num);
for(fact = 1 ; num > 0 ; num--)
fact *= num;
printf("\nFactorial is %ld", fact);
break;
}
case 7:
{
int day, month;
printf("\nEnter Date (dd mm yy) : ");
scanf("%d%d%d", &day, &month, &year);
if((day >= 1 && day <= 31) &&
(month == 1 || month == 3 || month == 5 || month == 7 ||
month == 8 || month == 10 || month == 12) &&
(year >= 1))
{
printf("%d / %d / %d is a valid date", day, month, year);
}
else if((day >= 1 && day <= 30) &&
(month == 4 || month == 6 || month == 9 || month == 11) &&
(year >= 1))
{
printf("%d / %d / %d is a valid date", day, month, year);
}
else if((day >= 1 && day <= 29) && (month == 2) &&
(year >= 1) &&
((year % 100 == 0 && year % 400 == 0) ||
(year % 100 != 0 && year % 4 == 0)))
{
printf("%d / %d / %d is a valid date", day, month, year);
}
else if((day >= 1 && day <= 28) && (month == 2))
printf("%d / %d / %d is a valid date", day, month, year);
else
printf("Invalid date");
break;
}
default :
printf("\nInvalid choice");
}
}while(choice != 8);

return 0;
}