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();
}