## Pages

### Palindrome Numbers

A palindrome number is a number such that if we reverse it, it will not change. For example some palindrome numbers examples are 121, 212, 12321, -454. To check whether a number is palindrome or not first we reverse it and then compare the number obtained with the original, if both are same then number is palindrome otherwise not. C program for palindrome number is given below.

## Palindrome number algorithm

1. Get the number from user.
2. Reverse it.
3. Compare it with the number entered by the user.
4. If both are same then print palindrome number
5. Else print not a palindrome number.

## Palindrome number program c

```#include

int main()
{
int n, reverse = 0, temp;

printf("Enter a number to check if it is a palindrome or not\n");
scanf("%d",&n);

temp = n;

while( temp != 0 )
{
reverse = reverse * 10;
reverse = reverse + temp%10;
temp = temp/10;
}

if ( n == reverse )
printf("%d is a palindrome number.\n", n);
else
printf("%d is not a palindrome number.\n", n);

return 0;
}```

### C program to reverse a number

This program reverse the number entered by the user and then prints the reversed number on the screen. For example if user enter 123 as input then 321 is printed as output. In the program we use modulus(%) operator to obtain the digits of a number. To invert number look at it and write it from opposite direction or the output of code is a number obtained by writing original number from right to left. To reverse or invert large numbers use long data type or long long data type if your compiler supports it, if you still have large numbers then use strings or other data structure.

## C programming code

```
#include

int main()
{
int n, reverse = 0;

printf("Enter a number to reverse\n");
scanf("%d",&n);

while (n != 0)
{
reverse = reverse * 10;
reverse = reverse + n%10;
n = n/10;
}

printf("Reverse of entered number is = %d\n", reverse);

return 0;
}```

### C program to swap two numbers

C program to swap two numbers with and without using third variable, swapping in c using pointers, functions (Call by reference) and using bitwise XOR operator, swapping means interchanging.
For example if in your c program you have taken two variable a and b where a = 4 and b = 5, then before swapping a = 4, b = 5 after swapping a = 5, b = 4
In our c program to swap numbers we will use a temp variable to swap two numbers.

## Swapping of two numbers in c

```#include

int main()
{
int x, y, temp;

printf("Enter the value of x and y\n");
scanf("%d%d", &x, &y);

printf("Before Swapping\nx = %d\ny = %d\n",x,y);

temp = x;
x    = y;
y    = temp;

printf("After Swapping\nx = %d\ny = %d\n",x,y);

return 0;
}```

### C program to add n numbers

This c program add n numbers which will be entered by the user. Firstly user will enter a number indicating how many numbers user wishes to add and then user will enter n numbers. In the first c program to add numbers we are not using an array, and using array in the second code.

## C programming code

```#include

int main()
{
int n, sum = 0, c, value;

printf("Enter the number of integers you want to add\n");
scanf("%d", &n);

printf("Enter %d integers\n",n);

for (c = 1; c <= n; c++)
{
scanf("%d",&value);
sum = sum + value;
}

printf("Sum of entered integers = %d\n",sum);

return 0;
}```

### C program to find HCF and LCM

C program to find hcf and lcm: The code below finds highest common factor and least common multiple of two integers. HCF is also known as greatest common divisor(GCD) or greatest common factor(gcf).

## C programming code

```#include

int main() {
int a, b, x, y, t, gcd, lcm;

printf("Enter two integers\n");
scanf("%d%d", &x, &y);

a = x;
b = y;

while (b != 0) {
t = b;
b = a % b;
a = t;
}

gcd = a;
lcm = (x*y)/gcd;

printf("Greatest common divisor of %d and %d = %d\n", x, y, gcd);
printf("Least common multiple of %d and %d = %d\n", x, y, lcm);

return 0;
}```

### Factorial program in C

C code to find and print factorial of a number, three methods are given, first one uses for loop, second uses a function to find factorial and third using recursion. Factorial is represented using '!', so five factorial will be written as (5!), n factorial as (n!). Also
n! = n*(n-1)*(n-2)*(n-3)...3.2.1 and zero factorial is defined as one i.e. 0! = 1.

## Factorial program in c using for loop

Here we find factorial using for loop.
```#include

int main()
{
int c, n, fact = 1;

printf("Enter a number to calculate it's factorial\n");
scanf("%d", &n);

for (c = 1; c <= n; c++)
fact = fact * c;

printf("Factorial of %d = %d\n", n, fact);

return 0;
}```

### C program to check leap year

C program to check leap year: c code to check leap year, year will be entered by the user.

## C programming code

```#include

int main()
{
int year;

printf("Enter a year to check if it is a leap year\n");
scanf("%d", &year);

if ( year%400 == 0)
printf("%d is a leap year.\n", year);
else if ( year%100 == 0)
printf("%d is not a leap year.\n", year);
else if ( year%4 == 0 )
printf("%d is a leap year.\n", year);
else
printf("%d is not a leap year.\n", year);

return 0;
}```

### C program to perform Addition, Subtraction, Multiplication and Division

C program to perform basic arithmetic operations which are addition, subtraction, multiplication and division of two numbers. Numbers are assumed to be integers and will be entered by the user.

## C programming code

```#include

int main()
{
int first, second, add, subtract, multiply;
float divide;

printf("Enter two integers\n");
scanf("%d%d", &first, &second);

subtract = first - second;
multiply = first * second;
divide     = first / (float)second;   //typecasting

printf("Difference = %d\n",subtract);
printf("Multiplication = %d\n",multiply);
printf("Division = %.2f\n",divide);

return 0;
}```

### C program to check Odd or Even

In mathematics, in decimal number system even numbers are divisible by 2 while odd are not so we can use modulus operator(%) which returns remainder, For example 4%3 gives 1 ( remainder when four is divided by three). Even numbers are of the form 2*p and odd are of the form (2*p+1) where p is is an integer.

## C program to check odd or even using modulus operator

```#include

main()
{
int n;

printf("Enter an integer\n");
scanf("%d",&n);

if ( n%2 == 0 )
printf("Even\n");
else
printf("Odd\n");

return 0;
}```