C program to convert plain text to cipher text

#include<stdio.h>
#include<conio.h>
#include<string.h>
void main() {
        char plainText[100], cipherText[100], value;
        int i = 0, key;
        printf("Enter the plain text(all caps):");
        fgets(plainText, 100, stdin);
        printf("Enter the key to create cipher text(1 - 5):");
        scanf("%d", &key);
        plainText[strlen(plainText) - 1] = '\0';
        while (plainText[i] != '\0') {
                if ((plainText[i] + key) > 'Z') {
                        value = (plainText[i] + key) - 'Z';
                        cipherText[i] = 'A' + value - 1;
                } else {
                        cipherText[i] = plainText[i] + key;
                }
                i++;
        }

        cipherText[i] = '\0';

        printf("Resultant Cipher Text: %s\n", cipherText);
        i = 0;
        printf("Plain Text:");
        while (cipherText[i] != '\0') {
                if ((cipherText[i] - key) < 'A') {
                        printf("%c", 'Z' + 1 - ('A' - (cipherText[i] - key)));
                } else {
                        printf("%c", cipherText[i] - key);
                }
                i++;
        }
        printf("\n");
        getch();
  }