Picking from a text file at random?

[JafferAB]

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

[jim mcnamara]

#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]);
     }          
}

[JafferAB]

thnaks

[CornedBee]

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

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

[jim mcnamara]

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.

[CornedBee]

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