Missing Logic Looping Through Switch Statement

Applications Programming
1

Having trouble with the logic when looping over this switch case again:

for (j = 0; data[j] != 0; j++){
     switch(data[j]){

    case 'c': 
            output[j] = ranit(r_brace_array);
            break;
    case 'h': 
            output[j] = ranit(pipe_array);
            break;            
    case 'e':
            output[j] = ranit(tilday_array);
            break;
    case 's':
            output[j] = ranit(comma_array);
            break;
    default:    
            break;        
         }
     }


     for (i = 0; output != 0; i++) {
         printf("%x\n", output);
     }

It calls a function (ranit) that assigns a letter a random hex number from an array and it works fine. However, if I give this program the phrase 'cheese' you will noticed that '85f31aae' is displayed for every instance of the letter 'e':

$ ./test
Gimme something: cheese

a4d19a86
1ad33008
85f31aae
85f31aae
3927bca6
85f31aae

What I want is the function ranit() to be called again if a letter repeats. This way a repeating character does not get a repeating number. I tried making an additional outer loop, but the results did not change.

Again, had to post a code snippet due to length of code.

If anyone can help with me with the logic its greatly appreciated.

2

What is this?

ranit(tilday_array)

Maybe it should be:

ranit(tilda_array)

?

3

Wow... That was actually a bad copy paste while making a snipet to fit in this post. This is what I should have had:

for (j = 0; data[j] != 0; j++){
   switch(data[j]){
      case 'c':              output[j] = ranit(c_array);
             break;     
     case 'h':              output[j] = ranit(h_array);             
            break;                 
     case 'e':              output[j] = ranit(e_array);             
            break;
     case 's':              output[j] = ranit(s_array);             
            break;     
     default:                 
            break;                  
     }      
}       

for (i = 0; output != 0; i++) {          
     printf("%x\n", output);      
}

Hopefully that makes more sense now.

4

Why and how do you expect varying results i.e. non-repeating numbers when running functions with non-varying, constant parameters?

5

Maybe I should have posted more code. This is the function that is being called each time:

// Pull random array element to be called for each character.
int ranit(int char_array[]) {
    srand ( time(NULL) );
    int RandIndex = rand() % DATA_SIZE;

    return char_array[RandIndex];
}

It selects a random in the array being called and works.

In another function all the arrays mentioned have a random number with /dev/urandom generated and assigned to each element.

Sorry if I was vague. I just have about 600 lines of code now and was trying to narrow down what was relevant to fit here. My apologies.

6

Calling random seed repeatedly is sort of overdoing it - or, in your case, even counterproductive. Do it once at program startup - if at all necessary as the compiler / interpreter may do it for you.

I know you are compiling a (C) program. Just as a hint, man awk explicitly says

awk 'BEGIN {srand(NULL); for (i=1; i<=10; i++) print rand()}'
0.131538
0.755605
0.45865
0.532767
0.218959
0.0470446
0.678865
0.679296
0.934693
0.383502
awk 'BEGIN { for (i=1; i<=10; i++) {srand(NULL); print rand()}}'
0.131538
0.131538
0.131538
0.131538
0.131538
0.131538
0.131538
0.131538
0.131538
0.131538

Although you are calling srand() with a sort of random parameter, the current system epoch time, the execution will be that fast epoch seconds will not change - that's why you lose the random effect.

Just remove the srand() from your function.

2 Likes
7

That did indeed work!

$ ./test
Gimme something: cheese

b2f14f45
f21f4f7a
1c1bc775
20737099
af749247
327683d

I knew that srand was based off the system clock and calculated fractions of seconds. I just didn't realize that a loop could iterate that fast I guess.

This also solves other problems I was having this program. Much appreciated!