How can I hide a flag from `strings` command

I want to create RE CTF, that the user needs to discover which string he need to write in order to execute a function that will print the flag, but, with a simple strings command in shell, we can discover the flag in the printf function. So, how can we make this not to happen?

#include <stdio.h>

void print_flag() {
    printf("secret_string discovered. flag: {eAsy_p3asy}");
}

int main()
{
    int c;
    c = getchar();
    while (c != 'secret_string') {
        putchar(c);
        c = getchar();
    }
    print_flag();
    return 0;
}

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Author: ArlichBachman