My cipher.txt file

#include<stdio.h>

int main()
{
    //ask the user what they want to encrypt or decrypt a string
    printf("Do you want to encrypt or decrypt a string? (e/d): ");
    char choice;
    scanf("%c", &choice);

    //if the user wants to encrypt, then use cipher.txt to encrypt the string
    if (choice == 'e')
    {
        //ask the user for the string they want to encrypt
        printf("Enter the string you want to encrypt: ");
        char string[100];
        scanf("%s", string);

        //open cipher.txt
        FILE* cipher;
        cipher = fopen("cipher.txt", "r");

        //read the cipher.txt file
        char cipherText[26];
        fscanf(cipher, "%s", cipherText);

        //close cipher.txt
        fclose(cipher);

        //encrypt the string
        int i;
        for (i = 0; i < 100; i++)
        {
            if (string[i] == '\0')
            {
                break;
            }
            else if (string[i] >= 'a' && string[i] <= 'z')
            {
                string[i] = cipherText[string[i] - 'a'];
            }
            else if (string[i] >= 'A' && string[i] <= 'Z')
            {
                string[i] = cipherText[string[i] - 'A'] - 32;
            }
        }

        //print the encrypted string
        printf("The encrypted string is: %s: ", string);


    }
    //if the user chooses decryption, then decrypt the string
    else if (choice == 'd')
    {
        //ask the user for the string they want to decrypt
        printf("Enter the string you want to decrypt: ");
        char string[100];
        scanf("%s", string);

        //open cipher.txt
        FILE* cipher;
        cipher = fopen("cipher.txt", "r");

        //read the cipher.txt file
        char cipherText[26];
        fscanf(cipher, "%s", cipherText);

        //close cipher.txt
        fclose(cipher);

        //decrypt the string
        int i;
        for (i = 0; i < 100; i++)
        {
            if (string[i] == '\0')
            {
                break;
            }
            else if (string[i] >= 'a' && string[i] <= 'z')
            {
                string[i] = cipherText[string[i] - 'a'];
            }
            else if (string[i] >= 'A' && string[i] <= 'Z')
            {
                string[i] = cipherText[string[i] - 'A'] - 32;
            }
        }

        //print the decrypted string
        printf("The decrypted string is: %s", string);

    }
}

我试着打开并使用Cipher.txt文件来交换字母并加密像hello这样的简单单词，并且能够通过输入密码文本来解密它们。Cipher.txt文件的编写目的是交换字母：
H、X、E、P、L、R、O、Q
我不知道如何让我的程序读取该文件，并与给定文件交换字母