Spaces shouldn't be counted to string length - c

Question

This code gets user input then 256 % length of string is used. If the result is 3 and the input is abc the output is bcd. This works fine. However if the input is for example "hey whatsup" the length is 11 and it should be 10 because the space shouldn't be included for the length.
How can I programm this code so it dosen't count space to the length?
Is it even possible to implement it while using fgets?
Thank you in advance.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main() {
char array[20];
int length = 0;
int i;
int key = 256;
printf("input: ");
fgets(array, 20, stdin);
length = strlen(array) - 1;
key = key % length;
if (key > 0) {
for (i = 0; i < length; i++) {
if (array[i] == ' ') {
printf("%c", array[i]);
continue;
}
array[i] = array[i] + key;
printf("%c", array[i]);
}
}
return 0;
}

Answer 1

1) If you don't want to include the spaces in the calculation of the key, you have to make your own function to calculate the number of spaces.
2) The code length = strlen(array) - 1; seems to "take care" of a '\n' in the end of the string. However, you can't be sure that there is a '\n'. You need to check for that first.
3) Doing key % 0 will be "bad" so check for that as well
The code could look something like:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int cnt_spaces(char* arr)
{
int res = 0;
while(*arr)
{
if (*arr == ' ')
{
++res;
}
++arr;
}
return res;
}
int main() {
char array[20];
int length = 0;
int i;
int key = 256;
printf("input: ");
fgets(array, 20, stdin);
length = strlen(array);
if (strlen(array) == 0) return 0; // or add error handling
// Remove \n if present
if (array[length-1] == '\n')
{
array[length-1] = '\0';
--length;
}
printf("len = %d\n", length);
int spaces = cnt_spaces(array);
printf("spaces = %d\n", spaces);
if (length == spaces) return 0; // or add error handling
key = key % (length - spaces);
printf("key = %d\n", key);
if (key > 0) {
for (i = 0; i < length; i++) {
if (array[i] != ' ') {
array[i] = array[i] + key;
}
printf("%c", array[i]);
}
}
return 0;
}
Example:
input: a b c
len = 5
spaces = 2
key = 1
b c d