CODEWITHSUNDEEP
c
mrew
mrew

Reputation: 21

C Program crashes after last input

C Program crashes after last scanf/last loop, (trivia game).

struct myQuiz*quizInput(int *nrQ)
{
    int i, nrofrecords = 0;
    struct myQuiz *Quiz = (struct myQuiz*)malloc(sizeof (struct myQuiz)**nrQ);

    printf("How many Questions?\n");
    scanf_s("%d", nrQ);

    for (i = 0; i < *nrQ; i++) //for-loop för att skriva in påståenden
    {
        printf("Trivia input: ");
        fflush(stdin);
        fgets(Quiz[i].qQuest, 100, stdin);
        nrofrecords = nrofrecords + 1;
        fflush(stdin);

        printf("Enter answer '1'(yes) or '0' (no): ");
        scanf_s("%d", &Quiz[i].qAns);
        fflush(stdin);

        printf("Enter the difficulty (1-5)?: ");
        scanf_s("%d", &Quiz[i].qDiff);


    }
    return Quiz;
}

Upvotes: 1

Views: 105

Answers (3)

user3629249
user3629249

Reputation: 16540

the code is using some trash from nrQ for the malloc 
before nrQ variable is set.

returned values from I/O statements 
must be checked to assure successful operation.

the user prompts fail to clearly indicate what the user is to input

suggest:

    printf("Please indicate how many Questions you will enter?\n");
    if(1 != scanf_s("%d", nrQ))
    { // then, scanf_s failed
        perror( "scanf_s for number questions failed" );
        return( NULL );
    }

    // implied else, scanf_s successful

    struct myQuiz *Quiz = NULL;
    if( NULL == (Quiz = malloc(sizeof (struct myQuiz)*(*nrQ)) )) )
    { // then, malloc failed
        perror( "malloc array of struct myQuiz failed" );
        return( NULL );
    }

    // implied else, malloc successful

    printf("\nNote: max question length: %d\n", sizeof(struct myQuiz.qQuest) );

Upvotes: 1

Iharob Al Asimi
Iharob Al Asimi

Reputation: 53006

You must initialize *nrQ first

struct myQuiz*quizInput(int *nrQ)
{
    int i, nrofrecords = 0;
    struct myQuiz *Quiz; // = malloc(sizeof (struct myQuiz)**nrQ); you need to initialize *nrQ first

    printf("How many Questions?\n");
    scanf_s("%d", nrQ);

    Quiz = malloc(sizeof (struct myQuiz)**nrQ);
    for (i = 0; i < *nrQ; i++) //for-loop för att skriva in påståenden
    {
        printf("Trivia input: ");

        fgets(Quiz[i].qQuest, 100, stdin);
        nrofrecords = nrofrecords + 1;

        printf("Enter answer '1'(yes) or '0' (no): ");
        scanf_s("%d", &Quiz[i].qAns);

        printf("Enter the difficulty (1-5)?: ");
        scanf_s("%d", &Quiz[i].qDiff);
    }
    return Quiz;
}

Also

  1. Don't cast malloc
  2. Don't fflush(stdin)

Upvotes: 0

radar
radar

Reputation: 13425

nRQ is the input to the function and memory allocated based on this value

struct myQuiz *Quiz = (struct myQuiz*)malloc(sizeof (struct myQuiz)**nrQ);

Actual questions value is asked after the malloc, so if initial value passed to the function is less than questions, the memory corruption happens. you need to get the input first and then allocate the memory later.

printf("How many Questions?\n");
scanf_s("%d", nrQ);

Upvotes: 2

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