Write your own printf() function in C

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<stdio.h>
#include<stdarg.h>
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));b
reak;
case 's': s=va_arg(argp,char *); puts(s); break;
case 'u': u=va_arg(argp,argp, unsigned int); puts(convert(u
,10));break;
47
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);
}