Caesar code

#include<stdio.h>
#include<string.h>
#include<cs50.h>

int main()
{
    char input[100], ch;
    int i, key;

    printf("Enter a input to encrypt: ");
    input = get_string;


    printf("Enter key: ");
    scanf("%d", &key);

    for(i = 0; input[i] != '\0'; ++i){
        ch = input[i];

        if(ch >= 'a' && ch <= 'z'){
            ch = ch + key;

            if(ch > 'z'){
                ch = ch - 'z' + 'a' - 1;
            }

            input[i] = ch;
        }
        else if(ch >= 'A' && ch <= 'Z'){
            ch = ch + key;

            if(ch > 'Z'){
                ch = ch - 'Z' + 'A' - 1;
            }

            input[i] = ch;
        }
    }

    printf("Encrypted input: %s", input);

    return 0;
}