using rand() in a function in c

Question

I have made a function that creates a random number between 0 and 9 but when i call the function in main in a for loop with index i = 0 ; i < n ; i++ it prints 1 random number n types. but i want different values to be printed n times. here is the code which i made :-

    #include<stdio.h>
    #include<stdlib.h>
    #include<time.h>
    void random_variable() {
     int i;
     srand(time(NULL));
     i = rand()%10;
     printf("%d ",i);
    }
    main() {
     for(int j=0;j<10;j++) {
      random_variable();
     }
    }

output is this :-

please click on the link to see the output :- here instead of 8 ten times i needed 10 different values

Don't redo the `srand` inside the loop - do it once before looping. It'll cause it to get reseeded and because it can loop 10 times so quickly, it'll get reseeded to the same value each time. I won't get into the deficiencies of `rand` here. — Steve, Nov 16 '17 at 18:05

score 5 · Accepted Answer · answered Nov 16 '17 at 18:06

5

srand() initializes the PRNG (pseudo random number generator) of your standard C library. A PRNG works by applying more-or-less complicated arithmetic operations to a value stored internally and returning part of the result as the next "random" number. srand() sets this internal state.

If you call srand() every time in your function, you won't get (sensible) random numbers because the internal state is reset every time. Call it once your program starts.

answered Nov 16 '17 at 18:06

okk. if i am using rand() two times to create two different sets of random number then also i have to use srand() once? – Nehal Birla Nov 16 '17 at 18:20
@NehalBirla I thought I explained this ... – Nov 17 '17 at 07:57

score 2 · Answer 2 · answered Nov 16 '17 at 18:06

2

srand() seeds your random numbers. You want to do this once, not every time.

    #include<stdio.h>
    #include<stdlib.h>
    #include<time.h>
    void random_variable() {
       int i;
       i = rand()%10;
       printf("%d ",i);
    }
    main() {
       srand(time(NULL));
       for(int j=0;j<10;j++) {
          random_variable();
       }
    }

answered Nov 16 '17 at 18:06

ale10ander

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if i use rand() two times i the function to create two different sets of random numbers then also i have to use srand() only once – Nehal Birla Nov 16 '17 at 18:23
Yes. Almost always, you want to call srand() ONCE per program. – ale10ander Nov 16 '17 at 18:29

using rand() in a function in c

2 Answers2