C freeing up dynamically allocated structure array

Question

Excuse me if this has already been discussed to death but I cannot seem to find anything that relates to the issue I am having. In the code below I am trying to create an array of structures that will be passed along to many different functions. I need to dynamically allocate the array as it varies based on the number of instructions the user inputs. I am not sure if my declaration of the variable of my use of malloc() is incorrect but on every run I experience a break point on the free(instruction) line. I have also tried placing the free(instruction) line outside of the if statement but it yields the same result.This is a homework assignment and any hints or explanation will be greatly appreciated.

struct instructions
{
    char destination_register[3],
        reg1[3],
        reg2[3];        //declaration of destination and source registers.
    int delay;
};

struct instructions* instruction;

int main() {

    int input=0;
    char test1[2];
    int test,numberofinstructions=0;

    do {
        printf ("Pipelined instruction performance\n"
                "1) Enter instructions\n"
                "2) Determine when instructions are fetched\n"
                "3) Exit\n"
                "Enter selection : ");
        scanf("%d",&input);
        if (input==1) {
            printf ("Enter number of instructions: ");
            scanf ("%d", &numberofinstructions);

            instruction = (struct instructions*) malloc(numberofinstructions + 
                            1 * sizeof(struct instructions));
            enterinstructs (instruction, numberofinstructions);

            printf("\n");
            free (instruction);
        }
    } while (input != 3);

    return 1;
}

Answer 1

I don't think that you want to this:

instruction = (struct instructions*) malloc(numberofinstructions + 1 * sizeof(struct instructions));

Here what happened is you allocated space sizeof(struct instructions) + numberofinstructions Which is meaningless.

What you want to do is probably:

instruction = (struct instructions*) malloc((numberofinstructions + 1) * sizeof(struct instructions));