C Programming Practice: 15 Exercises from Basics to Pointers

Take an integer input representing an amount in "cent" (e.g. 485). Calculate how many 25cent, 10cent, 5cent, and 1cent coins are needed. Pass the remainder to the next denomination.

Input : 485

Output:

25 cent: 19

10 cent: 1

5 cent: 1

1 cent: 0

---

#include <stdio.h>

int main() {

int amount;

printf("Enter amount in cent: ");

scanf("%d", &amount);

printf("25 cent: %d\n", amount / 25); amount %= 25;

printf("10 cent: %d\n", amount / 10); amount %= 10;

printf(" 5 cent: %d\n", amount / 5); amount %= 5;

printf(" 1 cent: %d\n", amount);

return 0;

}

Read a temperature in Celsius. Print the Fahrenheit and Kelvin equivalents.

F = C × 9/5 + 32

K = C + 273.15

Input : 100

Output:

Fahrenheit: 212.00

Kelvin : 373.15

---

#include <stdio.h>

int main() {

float c, f, k;

printf("Celsius: ");

scanf("%f", &c);

f = c * 9.0f / 5.0f + 32;

k = c + 273.15f;

printf("Fahrenheit: %.2f\n", f);

printf("Kelvin : %.2f\n", k);

return 0;

}

Read a single character. Print its ASCII value, the character before it, and the character after it.

Input : M

Output:

Character : M

ASCII : 77

Previous : L (76)

Next : N (78)

---

#include <stdio.h>

int main() {

char c;

printf("Character: ");

scanf(" %c", &c);

printf("Character : %c\n", c);

printf("ASCII : %d\n", c);

printf("Previous : %c (%d)\n", c-1, c-1);

printf("Next : %c (%d)\n", c+1, c+1);

return 0;

}

Read a 3-digit integer. Extract each digit and print their sum.

Input : 357

Output:

Hundreds : 3

Tens : 5

Units : 7

Sum : 15

---

#include <stdio.h>

int main() {

int n, h, t, u;

printf("3-digit number: ");

scanf("%d", &n);

h = n / 100;

t = (n / 10) % 10;

u = n % 10;

printf("Hundreds : %d\n", h);

printf("Tens : %d\n", t);

printf("Units : %d\n", u);

printf("Sum : %d\n", h + t + u);

return 0;

}

Read two words. Print the length of each, which comes first alphabetically, and whether they are identical.

Input : masa kasa

Output:

masa : 4 chars

kasa : 4 chars

Alphabetically first: kasa

Same word: No

---

#include <stdio.h>

#include <string.h>

int main() {

char a[50], b[50];

printf("Word 1: "); scanf("%s", a);

printf("Word 2: "); scanf("%s", b);

printf("%s : %zu chars\n", a, strlen(a));

printf("%s : %zu chars\n", b, strlen(b));

int cmp = strcmp(a, b);

if (cmp < 0) printf("Alphabetically first: %s\n", a);

else if (cmp > 0) printf("Alphabetically first: %s\n", b);

else printf("They are in the same position\n");

printf("Same word: %s\n", cmp == 0 ? "Yes" : "No");

return 0;

}

Read 5 exam scores (0–100). Calculate the average, assign a letter grade, and count passed/failed subjects. Passing score is 50.

Letter grades: 90+ AA, 80+ BA, 70+ BB, 60+ CB, 50+ CC, below → FF

Input : 75 88 42 95 60

Output:

Average: 72.00

Grade : BB

Passed : 4

Failed : 1

---

#include <stdio.h>

int main() {

int scores[5], i, passed = 0;

float total = 0, avg;

for (i = 0; i < 5; i++) {

printf("Score %d: ", i+1);

scanf("%d", &scores[i]);

total += scores[i];

if (scores[i] >= 50) passed++;

}

avg = total / 5;

printf("Average: %.2f\n", avg);

if (avg >= 90) printf("Grade: AA\n");

else if (avg >= 80) printf("Grade: BA\n");

else if (avg >= 70) printf("Grade: BB\n");

else if (avg >= 60) printf("Grade: CB\n");

else if (avg >= 50) printf("Grade: CC\n");

else printf("Grade: FF\n");

printf("Passed: %d\nFailed: %d\n", passed, 5 - passed);

return 0;

}

Read a word. Write a function that reverses it in-place using pointer parameters — no extra array. Print the original and the reversed version.

Input : programming

Output:

Original : programming

Reversed : gnimmargorp

---

#include <stdio.h>

#include <string.h>

void reverse(char *s) {

char *start = s;

char *end = s + strlen(s) - 1;

char tmp;

while (start < end) {

tmp = *start;

start = end;

*end = tmp;

start++;

end--;

}

}

int main() {

char word[100];

printf("Word: ");

scanf("%s", word);

printf("Original : %s\n", word);

reverse(word);

printf("Reversed : %s\n", word);

return 0;

}

Define a struct for a product: name, price, and stock. Read 4 products. Calculate the total inventory value (price × stock), find the most expensive product, and list any with stock below 5.

Output:

Total value : 694.50

Most expensive : Cheese (45.00)

Low stock (<5) :

Milk (3)

Yogurt (4)

---

#include <stdio.h>

typedef struct {

char name[30];

float price;

int stock;

} Product;

int main() {

Product p[4];

int i, maxIdx = 0;

float total = 0;

for (i = 0; i < 4; i++) {

printf("\nName : "); scanf("%s", p[i].name);

printf("Price : "); scanf("%f", &p[i].price);

printf("Stock : "); scanf("%d", &p[i].stock);

total += p[i].price * p[i].stock;

if (p[i].price > p[maxIdx].price) maxIdx = i;

}

printf("\nTotal value : %.2f\n", total);

printf("Most expensive : %s (%.2f)\n", p[maxIdx].name, p[maxIdx].price);

printf("Low stock (<5) :\n");

for (i = 0; i < 4; i++)

if (p[i].stock < 5)

printf(" %s (%d)\n", p[i].name, p[i].stock);

return 0;

}

Read 6 integers into an array. Write two functions — int* find_max(int arr, int n) and int find_min(int *arr, int n) — each returning a pointer to the target element. Print the values and their index positions.

Input : 4 9 2 7 1 6

Output:

Max: 9 (index 1)

Min: 1 (index 4)

---

#include <stdio.h>

int* find_max(int *a, int n) {

int *m = a;

for (int i = 1; i < n; i++)

if (*(a+i) > *m) m = a+i;

return m;

}

int* find_min(int *a, int n) {

int *m = a;

for (int i = 1; i < n; i++)

if (*(a+i) < *m) m = a+i;

return m;

}

int main() {

int arr[6], i;

for (i = 0; i < 6; i++) {

printf("Number %d: ", i+1);

scanf("%d", &arr[i]);

}

int *mx = find_max(arr, 6);

int *mn = find_min(arr, 6);

printf("Max: %d (index %ld)\n", *mx, mx - arr);

printf("Min: %d (index %ld)\n", *mn, mn - arr);

return 0;

}

Define an enum for three traffic light colors. The user picks one (1/2/3). Print what the light means and what comes next.

Input : 2

Output:

Meaning : Prepare

Next : Green

---

#include <stdio.h>

typedef enum { RED=1, YELLOW, GREEN } Light;

int main() {

int choice;

printf("1-Red 2-Yellow 3-Green\nChoice: ");

scanf("%d", &choice);

Light l = (Light)choice;

const char meaning, next;

switch (l) {

case RED: meaning="Stop"; next="Yellow"; break;

case YELLOW: meaning="Prepare"; next="Green"; break;

case GREEN: meaning="Go"; next="Red"; break;

default: meaning="Invalid"; next="-";

}

printf("Meaning : %s\n", meaning);

printf("Next : %s\n", next);

return 0;

}

Read a 3×3 matrix. Compute its transpose. Use pointer arithmetic syntax ((A+i)+j) in your loops — no plain bracket notation inside the loops.

Input: Output (Transpose):

1 2 3 1 4 7

4 5 6 2 5 8

7 8 9 3 6 9

---

#include <stdio.h>

int main() {

int A[3][3], T[3][3], i, j;

printf("Enter 3x3 matrix (row by row):\n");

for (i = 0; i < 3; i++)

for (j = 0; j < 3; j++)

scanf("%d", *(A+i)+j);

for (i = 0; i < 3; i++)

for (j = 0; j < 3; j++)

T[j][i] = A[i][j];

printf("\nOriginal:\n");

for (i = 0; i < 3; i++) {

for (j = 0; j < 3; j++) printf("%3d", ((A+i)+j));

printf("\n");

}

printf("\nTranspose:\n");

for (i = 0; i < 3; i++) {

for (j = 0; j < 3; j++) printf("%3d", T[i][j]);

printf("\n");

}

return 0;

}

Read a word. Write a function that checks if it's a palindrome using two pointers walking inward from both ends. The check must be case-insensitive.

Input: Kayak → Palindrome!

Input: Elma → Not a palindrome.

---

#include <stdio.h>

#include <string.h>

#include <ctype.h>

int is_palindrome(char *s) {

char *left = s;

char *right = s + strlen(s) - 1;

while (left < right) {

if (tolower(*left) != tolower(*right)) return 0;

left++;

right--;

}

return 1;

}

int main() {

char word[100];

printf("Word: ");

scanf("%s", word);

if (is_palindrome(word))

printf("Palindrome!\n");

else

printf("Not a palindrome.\n");

return 0;

}

Define a union that stores 4 bytes as both an unsigned int and a 4-element unsigned char array. Read an IPv4 address, store each octet in the char array, print the packed integer value, then reconstruct the IP from it.

Input : 192.168.1.1

Output:

Packed : 16885952

Unpacked: 192.168.1.1

---

#include <stdio.h>

union IP {

unsigned int packed;

unsigned char octet[4];

};

int main() {

union IP ip;

int a, b, c, d;

printf("IP address (a.b.c.d): ");

scanf("%d.%d.%d.%d", &a, &b, &c, &d);

ip.octet[0] = (unsigned char)a;

ip.octet[1] = (unsigned char)b;

ip.octet[2] = (unsigned char)c;

ip.octet[3] = (unsigned char)d;

printf("Packed : %u\n", ip.packed);

printf("Unpacked: %d.%d.%d.%d\n",

ip.octet[0], ip.octet[1],

ip.octet[2], ip.octet[3]);

return 0;

}

Write two functions to compute the Nth Fibonacci number: one iterative, one recursive. Read N (1–20), validate the range, print both results and how many steps/calls each method used.

N: 10

Output:

Iterative : 55 (9 steps)

Recursive : 55 (109 calls)

---

#include <stdio.h>

int call_count = 0;

long rec_fib(int n) {

call_count++;

if (n <= 1) return n;

return rec_fib(n-1) + rec_fib(n-2);

}

long iter_fib(int n, int *steps) {

if (n <= 1) { *steps = 0; return n; }

long a = 0, b = 1, c;

*steps = 0;

for (int i = 2; i <= n; i++) {

c = a + b; a = b; b = c;

(*steps)++;

}

return b;

}

int main() {

int n, steps;

printf("N (1-20): ");

scanf("%d", &n);

if (n < 1 || n > 20) {

printf("Invalid range!\n");

return 1;

}

long it = iter_fib(n, &steps);

long rec = rec_fib(n);

printf("Iterative : %ld (%d steps)\n", it, steps);

printf("Recursive : %ld (%d calls)\n", rec, call_count);

return 0;

}

Define a student struct with a name and 3 exam scores. Write a function that receives a pointer, computes the average, assigns the letter grade, and flags students needing a resit (average below 60). Run for 5 students, then list only those who need a resit.

Output:

Students needing resit:

- Ahmet (Avg: 45.00 | FF)

---

#include <stdio.h>

#include <string.h>

typedef struct {

char name[30];

float s1, s2, s3;

float avg;

char grade[3];

int resit;

} Student;

void evaluate(Student *s) {

s->avg = (s->s1 + s->s2 + s->s3) / 3.0f;

if (s->avg >= 90) strcpy(s->grade, "AA");

else if (s->avg >= 80) strcpy(s->grade, "BA");

else if (s->avg >= 70) strcpy(s->grade, "BB");

else if (s->avg >= 60) strcpy(s->grade, "CB");

else strcpy(s->grade, "FF");

s->resit = (s->avg < 60) ? 1 : 0;

}

int main() {

Student students[5];

int i;

for (i = 0; i < 5; i++) {

printf("\n--- Student %d ---\n", i+1);

printf("Name : "); scanf("%s", students[i].name);

printf("Exam 1: "); scanf("%f", &students[i].s1);

printf("Exam 2: "); scanf("%f", &students[i].s2);

printf("Exam 3: "); scanf("%f", &students[i].s3);

evaluate(&students[i]);

printf("Avg: %.2f Grade: %s\n",

students[i].avg, students[i].grade);

}

printf("\nStudents needing resit:\n");

int any = 0;

for (i = 0; i < 5; i++) {

if (students[i].resit) {

printf(" - %s (Avg: %.2f | %s)\n",

students[i].name,

students[i].avg,

students[i].grade);

any++;

}

}

if (!any) printf(" None\n");

return 0;

}