Noob to c programming help!

// This function will shift the character by the determined amount
// For our purpose we are only concerned with the letters a - z
char ShiftCharacter(char unencrypt,int shift_value,int offset)
[
char encrypted_char = unencrypt;
int i;

// Capital A - Z
if(unencrypt >= 'A' && unencrypt 'Z')
[
encrypted_char = 'A';
]
]

]

// Lowercase a - z
else if(unencrypt >= 'a' && unencrypt 'z')
[
encrypted_char = 'a';
]
]
]

return encrypted_char;

]

// casear_cipher.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include
#include

// Declare the function
char ShiftCharacter(char unencrypt,int shift_value,int offset);


int main(int argc, char* argv[])
[

char buff[1024];
int shift_value;
int encrypt_text_length;
int i;

// Say hello
puts("**initializing.....**\n\n**linking..........**\n\n");
puts("Welcome agent Brown\n\n");
puts("You have accessed the Caesar Cipher program\n\n");
puts("Please enter the text you wish to encrypt: ");

// Get input from the user
// It is possible that the user may exceed our allocated space.
// We could address that but it would cloud the issue. TODO: for later
scanf("%s",&buff);

puts("\nEnter your encryption shift value (anything from +-1 to 25): ");
scanf("%d",&shift_value);

// We now have a string and a shift value
// TODO: Check for empty string and out of range value


// Determine how long the string is
encrypt_text_length = strlen(buff);

// Encrypted the text
for(i = 0; i < encrypt_text_length; i++)
[
buff = ShiftCharacter(buff,shift_value,i);
]

// Display the encrypted text for the user
printf("\nYour encrypted text is: %s",buff);


return 0; /* indicate successful completeion */
]


// This function will shift the character by the determined amount
// For our purpose we are only concerned with the letters a - z
char ShiftCharacter(char unencrypt,int shift_value,int offset)
[
char encrypted_char;
int alphanumber; // The character as a number ( A = 1, B = 2, Z = 26 etc.)

// Capital A - Z
if(unencrypt >= 'A' && unencrypt = 'a' && unencrypt