Exam Prep: Prelims & Finals

This module preps you for both CP2 major exams. The prelim covers Lessons 1 to 3: Arrays in Depth, Strings and Character Arrays, and Pointers. The final covers Lessons 4 to 7 (Structures, File Handling, Recursion, Searching and Sorting) plus some cumulative review. This section and the two prelim mock exams below focus on Lessons 1 to 3.

How a CP2 Prelim on Lessons 1 to 3 Is Usually Structured

Different professors shuffle the weights, but almost every CP2 prelim on arrays, strings, and pointers is built from the same four parts:

Tracing plus programming is usually more than half the exam. You cannot pass by memorizing definitions alone: you have to practice running code on paper and writing small functions without notes.

Your Exact Memorize List

If you can do all ten of these cold, you are ready:

1. Passing an array passes its address. Call with the name alone, f(scores, n), and the function can change the caller's array. Mark read-only parameters const.
2. Always pass the size. Inside the function, sizeof a gives the size of an address, not the array. sizeof a / sizeof a[0] only works where the array is declared.
3. Linear search returns the index of the first match, or -1. The return -1 goes after the loop. Up to n comparisons, and the array does not need to be sorted.
4. Max/min patterns: keep the position, start from the first element. > keeps the first maximum, >= keeps the last. Reverse in place swaps a[i] with a[n - 1 - i] for only n / 2 passes.
5. 2-D arrays are stored row by row: t[r][c] sits at position r × COLS + c. A parameter may leave out the rows but must state the columns: int m[][COLS].
6. A string is a char array ending in '\0'. n characters need n + 1 slots. strlen counts the characters before '\0'; sizeof gives the whole array.
7. Never = or == on strings. Copy with strcpy, join with strcat, compare with strcmp(a, b) == 0. strcmp returns 0 for equal, negative if the first comes first, positive if it comes second.
8. '7' - '0' is the number 7, and value = value * 10 + (c - '0') builds a number from digit characters. <ctype.h> tests (isdigit, isalpha, isupper...) return non-zero for true.
9. Pointers: &x is the address of x, int *p = &x; makes p point to x, and *p = 25; changes x. Pass addresses (swap(&x, &y)) to let a function change the caller's variables or return more than one result.
10. Pointer arithmetic and arrays: p + 1 moves one element, not one byte. a[i] is exactly *(a + i), and q - p counts the elements between two pointers. An array name cannot be moved (a++ does not compile).

Top Mistakes That Cost Points

• Writing return -1; in an else inside the search loop, so only a[0] is ever checked.
• Calling print_array(scores[], n) or print_array(scores[4], n) instead of print_array(scores, n).
• Resetting a row or column total outside the outer loop, so every total includes the ones before it.
• Forgetting the '\0' when you copy or build a string one character at a time.
• Testing if (strcmp(a, b)) for "same text". That is true when the strings are different.
• Mixing up *p + 1 (the value plus one) with *(p + 1) (the next element), and *p++ (read, then move p) with (*p)++ (add one to the value).
• Writing through a pointer that was never given an address, or returning the address of a local variable.

Realistic 7-Day Study Plan

Each day names the exact lesson sections to read. Around 45 to 60 minutes a day is enough.

After Day 7, take Prelim Mock Exam A under exam conditions, check it with the answer key, re-read the sections behind every miss, then take Prelim Mock Exam B a day or two later.

How to Use This Module

• Free Practice Set (next section): 15 items sampling all seven lessons. Use it as a diagnostic: the answer key tells you which lesson each item came from.
• Prelim Mock Exams A and B: 25 items each, Lessons 1 to 3 only, in the same four parts as the table above. Do them on paper, timed, before opening the key.
• Answer Key with Explanations: every answer with a one-line reason, a trace table for the tricky tracing items, and a complete, tested program for every programming item. When you miss an item, find the exact line where your trace went wrong.
• Traps and final exam sections: after the prelim mocks, the rest of the module covers the common traps and the final exam on Lessons 4 to 7.

Fifteen genuine exam-style items sampling all seven lessons, about two per lesson. Do all fifteen before looking at the key, and treat it like the real thing: 30 minutes, no notes. The key tells you which lesson each item came from, so every miss points you to the lesson to review.

Part I, Multiple Choice (Items 1-4)

1. Given int scores[10]; and the function void show(const int a[], int n);, which call is correct?

• A. show(scores[10], 10);
• B. show(scores[], 10);
• C. show(scores, 10);
• D. show(&scores[], 10);

2. Given int x = 5; and int *p = &x;, which statement changes x to 9?

• A. p = 9;
• B. *p = 9;
• C. &x = 9;
• D. p* = 9;

3. Given the declarations below, which statement correctly sets the GWA through ps?

typedef struct {
    char name[30];
    double gwa;
} Student;

Student s;
Student *ps = &s;

• A. ps.gwa = 1.25;
• B. ps->gwa = 1.25;
• C. *ps.gwa = 1.25;
• D. ps->gwa == 1.25;

4. Which fopen mode erases the file if it already exists?

• A. "r"
• B. "a"
• C. "w"
• D. All three

Part II, Output Tracing (Items 5-9)

Write exactly what each fragment prints.

5.

int a[6] = {4, 9, 2, 9, 5, 1};
int i, pos = 0;
for (i = 1; i < 6; i++)
    if (a[i] >= a[pos])
        pos = i;
printf("%d %d", a[pos], pos);

6.

char s[20] = "Davao";
printf("%d %d", (int)strlen(s), (int)sizeof s);

7.

int a[4] = {2, 4, 6, 8};
int *p = a;
p += 2;
*p = *p * 3;
printf("%d %d", *p, *(p - 1));

8.

int f(int n) {
    if (n <= 1)
        return 1;
    return n + f(n - 2);
}

/* in main: */
printf("%d", f(7));

9. Bubble sort, ascending. One pass compares a[0] with a[1], then a[1] with a[2], and so on to the last pair, swapping whenever the left value is bigger. The array is {7, 3, 9, 2, 5}. Write the array after pass 1 and the number of swaps made.

Part III, Find the Error (Items 10-13)

For each one, say what is wrong and write the fix.

10. The user's name really is "Ana", but the program prints Who are you?.

char name[20] = "Ana";
if (name == "Ana")
    printf("Welcome, Ana!\n");
else
    printf("Who are you?\n");

11. Using the Student type from Item 3:

Student s;
s.name = "Liza";

12. This function is supposed to return 1 + 2 + ... + n.

int sumTo(int n) {
    return n + sumTo(n - 1);
}

13. This loop is supposed to print a text file one character at a time. fp was opened correctly.

char ch;
while ((ch = fgetc(fp)) != EOF)
    putchar(ch);

Part IV, Identification (Items 14-15)

14. Binary search for the key 31 in the sorted array {4, 9, 13, 18, 25, 31, 40}, using low = 0, high = 6 and mid = low + (high - low) / 2. List every index that becomes mid, in order, and give the value the search returns.

15. Given int t[4][5];, counting from 0, at what position in memory is t[2][3] stored?

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Answer Key

Scored 12 or better? You are on track. Below that, note which lessons your misses came from and re-read those lessons first. The full mock exams below (two for the prelim, two for the final, each with a complete answer key, trace tables and tested solutions) come with the subject unlock.