How to find GCD of two numbers in C Language

C Program for GCD of Two Numbers:

#include<stdio.h>
void main()
{
int x, y;
x = 12; y = 18;

while(x != y)
{
if(x > y)
x = x - y;
else
y = y - x;
}

printf("GCD of x and y is = %d", x);
}

How to find LCM of two numbers in C Language

C Program for LCM of Two Numbers:

#include<stdio.h>
void main()
{
int x, y, LCM;
x = 4; y = 9; LCM =1;

for(;;)
{
if(LCM % x != 0 || LCM % y != 0)
++LCM;
else
break;
}

printf("LCM of x and y is = %d", LCM);
}

How to swap two numbers in C Language

Using Two Variable:

Program 1:

#include<stdio.h>
#define SWAP(a,b) (a)^=(b)^=(a)^=(b)
void main()
{
int a,b;
a=12; b=17;
SWAP(a,b);
printf("a=%i,b=%i",a,b);
}

Program 2:

#include<stdio.h>
void main()
{
int a,b;
a=12; b=17;
a=a+b;
b=a-b;
a=a-b;
printf("a=%i,b=%i",a,b);
}

Using Third Variable:

#include<stdio.h>
void main()
{
int a,b,temp;
a=12; b=17; temp=0;
temp=a;
a=b;
b=temp;
printf("a=%i,b=%i",a,b);
}

How to print "Hello World" without using semicolon in main?

There are number of ways you can do it.

First Way:

#include<stdio.h>
void main()
{
if (printf("Hello World")) {}
}

Second Way:

#include<stdio.h>
void main()
{
while(!printf("Hello World")) {}
}

Third Way:

#include<stdio.h>
void main()
{
switch(printf("Hello World")) {}
}

Fourth Way:

#include<stdio.h>

#define PRINT printf("Hello World")

void main()

{

if(PRINT) {}

}