Floating Point Issues - General Questions

What will be the output of the program?

#include <stdio.h>
#include <math.h>

int main(void) {
    double x = 0.1 + 0.2;
    printf("%d\n", fabs(x - 0.3) < 1e-9);
    return 0;
}

What will be the output of the program?

#include <stdio.h>

int main(void) {
    float a = 0.1f;
    if (a == 0.1)
        printf("equal\n");
    else
        printf("not equal\n");
    return 0;
}

What will be the output of the program?

#include <stdio.h>

int main(void) {
    double d = 5.0 / 2;
    printf("%.2f\n", d);
    return 0;
}

What will be the output of the program?

#include <stdio.h>

int main(void) {
    printf("%d\n", (int)3.99);
    return 0;
}

How many significant decimal digits does a float typically hold?