Simple text based game in C

Question

After sticking with the same handful of languages for years, I decided to learn C.

I've written a guess the number game, where it generates a random number based on the difficulty level, and then you have 5 attempts of guessing the number.

If you guess incorrect, it will give you a clue by telling you if the answer is higher or lower than your last guess. I find the game to be pretty interactive, and wanted to get a code review to see how I could improve on it.

This is my first ever C program and I'm just looking to improve.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int generate_random_number(int min, int max) {
    srand ( time(NULL) );
    return min + (rand() % (max - min));
}

void play() {

    int difficulty = 1; // 1 = easy, 2 = medium, 3 = hard, 4 = insane

    printf("1 = EASY, 2 = MEDIUM, 3 = HARD, & 4 = INSANE\n");
    printf("What level would you like to play: ");

    scanf("%i", &difficulty);

    int min = 0;
    int max = 0;
    int random = 0;

    if (difficulty == 1) {
        min = 0;
        max = 25;

        printf("You have selected to play easy\n\n");
    }
    else if (difficulty == 2) {
        min = 0;
        max = 50;

        printf("You have selected to play medium\n\n");
    }
    else if (difficulty == 3) {
        min = 0;
        max = 75;

        printf("You have selected to play hard\n\n");
    }
    else if (difficulty == 4) {
        min = 0;
        max = 100;

        printf("You have selected to play insane\n\n");
    }

    random = generate_random_number(min, max);

    int tries = 5;
    int won = 0;

    while (tries > 0)
    {
        int guess = 1000000; // just so it doesn't accidentally equal to random

        printf("Guess a number %i to %i: ", min, max);
        scanf("%i", &guess);

        if (guess == random) {
            won = 1;
            break;
        }
        else {
            if (guess > random) {
                printf("Incorrect guess, the answer is lower than your guess!\n\n");
            }
            else {
                printf("Incorrect guess, the answer is higher than your guess!\n\n");
            }
        }

        tries -= 1;
    }

    if (won) {
        printf("Congratulations, you have won the game!");
    }
    else {
        printf("Sorry, you are out of tries.\n\n");
    }
}

int main() {
    while (1) {
        play();
    }

    return 0;
}

Answer 1

Good:

no warnings with -Wall -Wextra -pedantic with both gcc and clang, no memory leaks found with valgrind.

Bad:

use prototypes instead of declarations to give compiler a chance to issue warnings when an incorrect number of parameters is passed or incorrect types are passed:

void play(void)
int main(void)

You don't check if user passes correct acceptable difficulty level:

$ ./main
1 = EASY, 2 = MEDIUM, 3 = HARD, & 4 = INSANE
What level would you like to play: 6
Floating point exception
$ ./main
1 = EASY, 2 = MEDIUM, 3 = HARD, & 4 = INSANE
What level would you like to play: 0
Floating point exception

You don't check if user passes an integer in the first place:

$ ./main
1 = EASY, 2 = MEDIUM, 3 = HARD, & 4 = INSANE
What level would you like to play: a

will make your program go into an endless loop.

Suggested:

convert int difficulty = 1 into an en enum with additional DIFFICULTY_MAX and DIFFICULTY_MIN values, and check if value passed from the user is lower than DIFFICULTY_MAX and larger or equal to DIFFICULTY_MIN.

Use EXIT_SUCCESS to denote success at the end of main():

return EXIT_SUCCESS;

or just omit the return from main() - compiler will automatically return a success value if we run off the end.

Answer 2

int generate_random_number(int min, int max) {
    srand ( time(NULL) );
    return min + (rand() % (max - min));
}

You should only seed the random number generator once, at the start of main. In this case, if (for some reason) somebody played more than one round in a single second, both games would have the same number. Probably not a huge issue for this particular program, but something to be aware of.

Answer 3

if (difficulty == 1) {
else if (difficulty == 2) {
else if (difficulty == 3) {

This looks like switch (difficulty) might be more appropriate - perhaps with a default branch to catch out-of-range values.

Or, more simply, since we're just picking values, and min is always 0, just select from an array values (after verifying that the user's choice is in range):

int max[] = { 25, 50, 75, 100 };

In fact, with these values, we could simply multiply:

int max = 25 * difficulty;

---

scanf("%i", &difficulty);

Don't just discard the result from scanf() - always test that it converted as many values as you wanted. In this case,

if (scanf("%i", &difficulty) != 1) {
    fputs("Enter a number!\n", stderr);
    exit(EXIT_FAILURE);  /* or some better handling */
}

Similarly here:

    scanf("%i", &guess);

---

Finally, it would be polite to allow users to exit the game when they get bored of it (I know, I can't quite believe that might happen, either!).