check the given no is prime or not

void main()
{
int num,i,count=0;
clrscr();
printf("\nEnter a number:");
scanf("%d",&num);
for(i=1;i<=num;i++)
{
if(num%i==0)
count++;
}
if(count==2)
printf("%d is a prime number",num);
else
printf("%d is not a prime number",num);
getch();
}

Chech the given no is amstrong or not+

void main()
{
int num,r,sum=0,temp;
clrscr();
printf("\nEnter a number:-");
scanf("%d",&num);
temp=num;
while(num!=0)
{
r=num%10;
num=num/10;
sum=sum+(r*r*r);
}
if(sum==temp)
printf("\nThe number %d is an armstrong number",temp);
else
printf("\nThe number %d is not an armstrong number",temp);
getch();
}

g.c.d of two number

void main()
{
int n1,n2;
clrscr();
printf("\nEnter two numbers:");
scanf("%d %d",&n1,&n2);
while(n1!=n2)
{
if(n1>n2)
n1=n1-n2;
else
n2=n2-n1;
}
printf("\nGCD=%d",n1);
getch();
}

entered number is palindrome or not

void main()
{
int num,r,sum=0,temp;
clrscr();
printf("\nEnter a number:");
scanf("%d",&num);
temp=num;
while(num)
{
r=num%10;
num=num/10;
sum=sum*10+r;
}
if(temp==sum)
printf("\n%d is a palindrome",temp);
else
printf("\n%d is not a palindrome",temp);
getch();
}

Write ur own Printf() Function

This is again one of the most frequently asked interview questions. Here is a C program which implements a basic version of printf(). This is a really, really simplified version of printf(). Note carefully how floating point and other compilcated support has been left out. Also, note how we use low level puts() and putchar(). Dont make a fool of yourself by using printf() within the implementation of printf()!


#include
#include

main()
{
void myprintf(char *,...);
char * convert(unsigned int, int);
int i=65;
char str[]="This is my string";
myprintf("\nMessage = %s%d%x",str,i,i);
}

void myprintf(char * frmt,...)
{

char *p;
int i;
unsigned u;
char *s;
va_list argp;


va_start(argp, fmt);

p=fmt;
for(p=fmt; *p!='\0';p++)
{
if(*p=='%')
{
putchar(*p);continue;
}

p++;

switch(*p)
{
case 'c' : i=va_arg(argp,int);putchar(i);break;
case 'd' : i=va_arg(argp,int);
if(i<0){i=-i;putchar('-');}puts(convert(i,10));break;
case 'o': i=va_arg(argp,unsigned int); puts(convert(i,8));break;
case 's': s=va_arg(argp,char *); puts(s); break;
case 'u': u=va_arg(argp,argp, unsigned int); puts(convert(u,10));break;
case 'x': u=va_arg(argp,argp, unsigned int); puts(convert(u,16));break;
case '%': putchar('%');break;
}
}

va_end(argp);
}

char *convert(unsigned int, int)
{
static char buf[33];
char *ptr;

ptr=&buf[sizeof(buff)-1];
*ptr='\0';
do
{
*--ptr="0123456789abcdef"[num%base];
num/=base;
}while(num!=0);
return(ptr);
}

How do you initalize a Pointer inside a function

This is one of the very popular interview questions, so take a good look at it!.


myfunction(int *ptr)
{
int myvar = 100;
ptr = &myvar;
}

main()
{
int *myptr;
myfunction(myptr);

//Use pointer myptr.

}


Do you think this works? It does not!.


Arguments in C are passed by value. The called function changed the passed copy of the pointer, and not the actual pointer.


There are two ways around this problem

Method1

Pass in the address of the pointer to the function (the function needs to accept a pointer-to-a-pointer).


calling_function()
{
char *string;
return_string(/* Pass the address of the pointer */&string);
printf(?\n[%s]\n?, string);
}

boolean return_string(char **mode_string /*Pointer to a pointer! */)
{
*string = (char *) malloc(100 * sizeof(char)); // Allocate memory to the pointer passed, not its copy.
DISCARD strcpy((char *)*string, (char *)?Something?);
}



Method2

Make the function return the pointer.


char *myfunc()
{
char *temp = "string";
return temp;
}

int main()
{
puts(myfunc());
}

\

There are a number of ways one can reverse strings. Here are a few of them. These should be enough to impress the interviewer! The methods span from recursive to non-recursive (iterative).

Also note that there is a similar question about reversing the words in a sentence, but still keeping the words in place. That is


I am a good boy


would become


boy good a am I


This is dealt with in another question. Here I only concentrate on reversing strings. That is


I am a good boy


would become


yob doog a ma I



Here are some sample C programs to do the same


Method1 (Recursive)


#include

static char str[]="STRING TO REVERSE";

int main(int argc, char *argv)
{
printf("\nOriginal string : [%s]", str);

// Call the recursion function
reverse(0);

printf("\nReversed string : [%s]", str);
return(0);
}

int reverse(int pos)
{
// Here I am calculating strlen(str) everytime.
// This can be avoided by doing this computation
// earlier and storing it somewhere for later use.

if(pos<(strlen(str)/2))
{
char ch;

// Swap str[pos] and str[strlen(str)-pos-1]
ch = str[pos];
str[pos]=str[strlen(str)-pos-1];
str[strlen(str)-pos-1]=ch;

// Now recurse!
reverse(pos+1);
}
}





Method2


#include
#include
#include

void ReverseStr ( char *buff, int start, int end )
{
char tmp ;

if ( start >= end )
{
printf ( "\n%s\n", buff );
return;
}

tmp = *(buff + start);
*(buff + start) = *(buff + end);
*(buff + end) = tmp ;

ReverseStr (buff, ++start, --end );
}


int main()
{
char buffer[]="This is Test";
ReverseStr(buffer,0,strlen(buffer)-1);
return 0;
}




Method3


public static String reverse(String s)
{
int N = s.length();
if (N <= 1) return s;
String left = s.substring(0, N/2);
String right = s.substring(N/2, N);
return reverse(right) + reverse(left);
}





Method4

for(int i = 0, j = reversed.Length - 1; i < j; i++, j--)
{
char temp = reversed[i];
reversed[i] = reversed[j];
reversed[j] = temp;
}
return new String(reversed);





Method5


public static String reverse(String s)
{
int N = s.length();
String reverse = "";
for (int i = 0; i < N; i++)
reverse = s.charAt(i) + reverse;
return reverse;
}





Method6

public static String reverse(String s)
{
int N = s.length();
char[] a = new char[N];
for (int i = 0; i < N; i++)
a[i] = s.charAt(N-i-1);
String reverse = new String(a);
return reverse;
}