C program to encrypt a string.

Question: Write a program to crypt its input according to a specified transformation scheme. The transformation scheme will consist of two strings: a string of characters and then a string of replacement characters. The idea is that your program replaces every instance of the ith character in the initial string with the (i+2) character (of English alphabets) in the replacement string. When no substitution is defined for a character, the program just passes it through to the output unchanged. Blank spaces and the other symbols remains the same. The program should inform the user of any errors in the transformation scheme. Your program should display the phrase before and after the substitutions have been made.
Example:
Original String: I know C programming.
String after the transformation: K mpqy E rtqitcookpi.

Answer:

#include<stdio.h>
#include<conio.h>

void read_string(char str[]);
void crypt(char str[], int transform_scheme);

void main()
{
	int transform_scheme;
	char str[100];

	clrscr();

	printf("\nEnter a string (Not more than 100 chars): ");

	//Read data from the user
	read_string(str);
	printf("\nOriginal String is: %s\n", str);

	//Read transformation scheme from the user
	printf("\nEnter the transaformation scheme (In Integer): ");
	scanf("%d", &transform_scheme);

	//Logic to convert the input string to encrypted form
	crypt(str, transform_scheme);
	printf("\nConverted String is: %s\n", str);
	getch();
}

void read_string(char str[])
{
	int i, temp;

	i = 0;
	while((temp = getchar()) != '\n')
	{
		str[i] = temp;
		i = i+1;
	}
	str[i] = '\0';
}

void crypt(char str[], int transform_scheme)
{
	int i,len;
	len = strlen(str);

	for(i=0; i<len; i++)
	{
		if(str[i] >= 'A' && str[i] <= 'Z')
		{
			str[i] = str[i] + transform_scheme;

			if(str[i] > 'Z')
			{
				str[i] = 'A' + ((str[i] - 'Z') - 1);
			}

			if(str[i] < 'A')
			{
				str[i] = 'Z' - (('A' - str[i]) - 1);
			}
		}
		if(str[i] >= 'a' && str[i] <= 'z')
		{
			str[i] = str[i] + transform_scheme;

			if(str[i] > 'z')
			{
				str[i] = 'a' + ((str[i] - 'z') - 1);
			}

			if(str[i] < 'a')
			{
				str[i] = 'z' - (('a' - str[i]) - 1);
			}
		}
	}
}