Picking from a text file at random?

Im tryign to make my program (a trivia one) read from a text file, well, it reads the questions from the text file.

But im trying to make it pick the questions at random. I cant find any tutorials for this, so wondered if anyone here could help..

thanx

Code:

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#include <stdio.h>
void main(void){
  char arr[100][100];  // one hundred questions
  char tmp[100];
  int i,j;
  int q=(-1);
  FILE*in;
  in = fopen("myquestions.txt","r");
  if (ferror(in) || in ==NULL){
            perror("Error opening input file");
            exit(1);
  }
    memset (tmp,'\0',sizeof(tmp) );
  while (!feof(in) ){
            if(fgets(tmp,99,in)!=NULL) {
                  q++;
                  strcpy(arr(q),tmp); 
            }
    }          // you now have a char array of length q
    fclose(in);
    for (i=0;i<10;i++) { // ask 10 questions
          j = (int) ( ( (float)rand()/ (float)RAND_MAX ) *(float)(q +1) ) ;
          // j is a random value between  zero and q
          printf("question: %s ?\n", arr[j]);
    }         
}

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thnaks :D:D:D:D:D:D

Quote:

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j = (int) ( ( (float)rand()/ (float)RAND_MAX ) *(float)(q +1) ) ;

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what is the advantage of this (it's awfully slow...)

There is no great advantage to this, other than eliminating the use of more variables declared as float.

You're right - casting is very slow - but this app probably does one calculation like this every 30 seconds. It isn't in a loop executing at full cpu speed. If it were it would be a terrible choice.

I mean what is the advantage of this vs
int i = rand() % q;
?