C Program to work with strings without string functions

This simple program shows you how to find the string length, copy a string and concatenate two strings without using built-in string functions.

//Program to manipulate strings without string functions
#include<stdio.h>
#include<conio.h>
main()
{
  char *str1,*str2;
  int i,j, choice;

  clrscr();
  printf("1. String length\n");
  printf("2. String copy\n");
  printf("3. String Concat\n");
  printf("Enter choice\n");
  scanf("%d",&choice);
  switch (choice)
  {
    case 1: printf("\nEnter string\n");
   fflush(stdin);
   gets(str1);
   for(i=0;str1[i]!='\0';i++);
   printf("The length of the string  \"%s\" is %d",str1,i);
   break;

   case 2: printf("\nEnter string to be copied\n");
  fflush(stdin);
  gets(str1);
  for(i=0;str1[i]!='\0';i++)
     str2[i]=str1[i];
     str2[i]='\0';
  printf("String1 = %s",str1);
  printf("\nThe copied string str2 = %s", str2);
  break;

   case 3: printf("\nEnter string1 and string2\n");
  fflush(stdin);
  gets(str1);
  gets(str2);
  for(i=0;str1[i]!='\0';i++);

  for(j=0;str2[j]!='\0';j++)
  str1[i++]=str2[j];
  str1[i]='\0';
  printf("\nThe concatenated string is %s",str1);
  break;

   default: printf("\nWrong choice\n");
   }

   getch();
}

/*
OUTPUT
--------
1. String length
2. String copy
3. String Concat
Enter choice
3

Enter string1 and string2
good
morning

The concatenated string is goodmorning

1. String length
2. String copy
3. String Concat
Enter choice
1

Enter string
welcome
The length of the string  "welcome" is 7

1. String length
2. String copy
3. String Concat
Enter choice
2

Enter string to be copied
welcome
String1 = welcome
The copied string str2 = welcome
*/