Appending characters

[Koppis]

Hello!
The idea of my program is to ask each time for a character, to save it so I can add a new character that will be added after the first one etc. Then there's a choice to empty it or print it all.

So a example how it should work:
1) Input: H
*Choose 1) again*
1) Input: i
*Choose 3)*
it should print: Hi

It's not working how I want it to tho, I'd appreciate some help on what to do. Thank you!

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

int main(void) {
int choice;
char str[20] = {0};
char str1;

while(1) {
    printf("Menu\n1) Add char\n2)Empty all\n3)Print\n0)Stop\n");
    printf("Give your choice: "); //Asks the choice from the menu
    scanf("%i", &choice);

    if(choice == 1) { //This choice adds a letter to the (empty) string
        printf("Give a letter: ");
        scanf(" %c", &str1); 
        int len = strlen(str);
    str[len] = str1;
    str[len + 1] = '\0'; }

    else if(choice == 2) { //choice 2 clears the string
        printf("");
        scanf("%s", str1); }

    else if(choice == 3) { //choice 3 prints what's in the string
        printf("%s\n", str1); }

    else if(choice == 0) {
    printf("Wrong input!");
    break; }

    else { //if choice is wrong, it ends the program
        printf("Faulty input!\n");
        break; }

    }   }

[john.c]

#include <stdio.h>
#include <string.h>
  
int main() {
    char str[200] = {0};
    int len = 0;
 
    while (1) {
        int choice;
        printf("\n1) Add char\n2) Empty all\n3) Print\n0) Stop\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);
      
        if (choice == 1) { // add a letter to the string
            char ch;
            printf("Enter a letter: ");
            scanf(" %c", &ch); 
            str[len++] = ch;
            str[len] = '\0';
        }     
        else if (choice == 2) { // clear the string
            len = 0;
            str[0] = '\0';
        }     
        else if (choice == 3) // print what's in the string
            printf("%s\n", str);
        else if (choice == 0)
            break;
        else
            printf("Faulty input! Try again.\n");
    }
}