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Generating a pseudo-random number Necessary libraries: <stdlib.h> and <time.h> Seeding: srand(time(NULL)) We set the seed based on the current time NB! Time-dependent seed changes once a second. Don’t use it in a loop! Tip: use a fixed constant as seed to always test with the same set of “random” numbers Generating a random number: rand() function Function returns a random number The returned value is a positive integer The number is between 0 … RAND_MAX (the #define comes from stdlib.h library) 2018 Risto Heinsar

Sample code to get a pseudo-random number #include <stdio.h> #include <stdlib.h> #include <time.h>   int main(void) { srand(time(NULL)); // set the seed, we do this ONLY ONCE! int randNum; randNum = rand(); // call the random number function, store the return printf("max is %d\n", RAND_MAX); // largest possible random number (can’t be changed) printf(“Got: %d\n", randNum); // print out the number that rand() function returned printf(“Got: %d\n", rand()); // print out another number that rand() function returns printf(“Got: %d\n", rand() % 10); // numbers from 0 to 9 return 0; } 2018 Risto Heinsar

Lab task #1: lottery Lotto numbers should be in between 1 … 30 The user is asked for 6 numbers Program generates 10 numbers at random Display the winning numbers Check and print how many and which of the numbers matched If all 6 matched, congratulate the user on winning the jackpot Give your condolence when none of the numbers matched Advanced: make sure none of the user entered and generated numbers occur twice 2018 Risto Heinsar