Week 9: Pointer — Solution

Exercise Solutions

Exercise 1: Change multiple values in a function using pointers

#include <stdio.h>

void addOne(int *a, int *b, int *c, int *d) {
    (*a)++;
    (*b)++;
    (*c)++;
    (*d)++;
}

int main(void) {
    int a = 1, b = 2, c = 3, d = 4;

    printf("=====before change=====\n");
    printf("a = %d, b = %d, c = %d, d = %d\n", a, b, c, d);

    addOne(&a, &b, &c, &d);

    printf("=====after change=====\n");
    printf("a = %d, b = %d, c = %d, d = %d\n", a, b, c, d);
    return 0;
}

Example Output:

=====before change=====
a = 1, b = 2, c = 3, d = 4
=====after change=====
a = 2, b = 3, c = 4, d = 5

---

Exercise 2: Find the Maximum Value Using Pointers

#include <stdio.h>

int main(void) {
    int array[] = {3, 2, 4, 22, 15, 6, 8};
    int n = sizeof(array) / sizeof(array[0]);

    int *p = array;
    int max = *p;

    for (int i = 1; i < n; i++) {
        if (*(p + i) > max) {
            max = *(p + i);
        }
    }

    printf("Maximum value = %d\n", max);
    return 0;
}

Example Output:

Maximum value = 22

---

Exercise 3: Find an Alphabet in a Word (pointer arithmetic)

#include <stdio.h>

int main(void) {
    char letter;
    char word[100];

    printf("Please input the alphabet you want: ");
    scanf(" %c", &letter);
    printf("Please input the word you want: ");
    scanf("%s", word);

    char *p = word;
    int found = 0;
    while (*p != '\0') {
        if (*p == letter) {
            found = 1;
            break;
        }
        p++;
    }

    if (found) printf("found %c!\n", letter);
    else       printf("cannot find %c!\n", letter);

    return 0;
}

Example Output:

Please input the alphabet you want: i
Please input the word you want: apple
cannot find i!

Please input the alphabet you want: a
Please input the word you want: grammer
found a!