ACROMATIC STRING(PRINTING INITIALS)

void main()
{
int i=0,j=0;
char *str1,*str2,*str3;
clrscr();
puts("Enter first string");
gets(str1);
puts("Enter second string");
gets(str2);
printf("Before concatenation the strings are\n");
puts(str1);
puts(str2);
while(*str1)
{
str3[i++]=*str1++;
}
while(*str2)
{
str3[i++]=*str2++;
}
str3[i]='\0';
printf("After concatenation the strings are\n");
puts(str3);
getch();
}