Midterm 1

1. Topics
2. Expected Questions
3. Example Coding Problem
- 3.1. My Solution

Homeworks and in-class assignments are where midterm questions are tested.

1. Topics

Make Variables
The build/compilation sequence
Size of all data types
All keywords except union and volatile
Precedence vs. Associativity
The sequence points (; and ,)
Return values of the I/O functions
- prinf returns the amount of characters that it wrote
- scanf returns the number of successful conversions it made
- getchar returns an int to circumvent the inband-signaling of an incorrect character
- putchar returns the value of the character written
Passing pointers and pointers to pointers
Endians
Structs
When are read only strings read only?
Storage Class
gdb commands

2. Expected Questions

Changing the value of a pointer in a function
Precedence between * (dereference) and other operators (specfically . and ++)

3. Example Coding Problem

25 points: Coding question #1 – Write the call to a function swapIfWrong and write the function. There are two int pointers and a function pointer available in the calling function to be passed to swapIfWrong. How the pointers and function pointer got their values is not shown and is not your concern; assume valid values are present in all 3 and that those values were assigned where comment #3 is. After swapIfWrong runs, the goodptr will point to the better value and the badptr will point to the worse value. Do not change the values; only change the pointers if they need it. To compare the values, use the is_better comparison function. The is_better function returns a true value if the goodvalue it is passed is better than the badvalue it is passed.

Be very careful about type. Think about what it means when a function needs to change something. The structure needed here is somewhat simple, the types of the variables require great care.

Again: When swapIfWrong returns, goodptr and badptr in the calling function now point where they should.

Your coding task:

Fill out the arguments to swapIfWrong in the calling function (complete the line between comment #3 and #4).
Fill out the parameter list for swapIfWrong (just below comment #5).
Write the code for swapIfWrong (between comment #6 and #7).

/* #1 assume are required #includes and declarations have been made */
typedef int (*comparison_function)(int goodvalue, int badvalue);
int CallingFunction() {
    int *goodptr, *badptr;
    comparison_function is_better;
    /* #2 code you did not have to write has given a value to
    ** goodptr, badptr, and is_better. That code would be here.*/
    /* #3 fill in the function parameters below */
    swapIfWrong(/* enter parameters */);
    /* #4 the line above is all you do in the calling function */
}
/* put your function below here */
void swapIfWrong() {
}

3.1. My Solution

#include <stdio.h>
/* #1 assume are required #includes and declarations have been made */
typedef int (*comparison_function)(int goodvalue, int badvalue);
/* put your function below here */
void swapIfWrong(int **good, int **bad, comparison_function comp) {
    int *temp;

    if (!comp(**good, **bad)) {
        /* I aussume this means that we have a bad value */
        temp = *good;
        *good = *bad;
        *bad = temp;
    }

}


int CallingFunction() {
    int *goodptr, *badptr;
    comparison_function is_better;
    /* #2 code you did not have to write has given a value to
    ** goodptr, badptr, and is_better. That code would be here.*/
    /* #3 fill in the function parameters below */
    swapIfWrong(&goodptr, &badptr, is_better);
    /* #4 the line above is all you do in the calling function */
}
/* I need a comparison function */
int greater(int big, int small) {
    printf("Comparing %d to %d\n", big, small);
    return (big > small);
}

void main() {
    int *goodptr, *badptr;
    comparison_function is_better;
    int bigi = 4, smalli=20;
    goodptr = &bigi;
    badptr = &smalli;
    is_better = greater;
    printf("Before *good is %d and *bad is %d\n", *goodptr, *badptr);
    /* pass in the address of things I need to change */
    swapIfWrong(&goodptr, &badptr, is_better);
    printf("After *good is %d and *bad is %d\n", *goodptr, *badptr);
    printf("Hello!");
}

Midterm 1

Table of Contents

1. Topics

2. Expected Questions

3. Example Coding Problem

3.1. My Solution