clarification for RAND_MAX and rand() in c stdlib.h

Question

why does the following c code produce real numbers only ranging between 0 and 1(eg: 0.840188,0.394383...etc) for double a,b when the value for RAND_MAX appears to be 0.000000 . Shouldn't RAND_MAX set the maximum value for the number generated by rand() function ?

    #include <stdio.h>
    #include <stdlib.h>
    int main()
    {

    double a,b,c;
    for (int i=0;i<100;i++){
    a=(double)rand()/(double)RAND_MAX;
    b=(double)rand()/(double)RAND_MAX;
    c=a-b;
    printf("itteration : %d values a=%f,b=%f,c=%f, RAND_MAX=%f \n",i,a,b,c,RAND_MAX);
    }  
    return 0;
    }

Answer 1

RAND_MAX is an integral constant, but you are printing it using the %f specifier (used for double), which is undefined behavior (and in your case happens to print 0). Use %d and you'll see the actual value of RAND_MAX.

By the way, pretty much any decent compiler will warn you about that invalid printf if you crank the warnings high enough. Make sure to do so, C and C++ are full of traps enough, at least let the compiler help you when it can.