// Q1: Define PI using macro and find perimeter

#include <stdio.h>

#define PI 3.14159

int main() {

float radius, perimeter;

printf("Enter radius: ");

scanf("%f", &radius);

perimeter = 2 * PI * radius;

printf("Perimeter = %.2f\n", perimeter);

return 0;

// Q2: Copy non-zero elements, sum them (Dynamic Memory)

#include <stdio.h>

#include <stdlib.h>

int main() {

int n, i, *a, *b, count = 0, sum = 0;

printf("Enter number of elements: ");

scanf("%d", &n);

a = malloc(n * sizeof(int));

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

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

if (a[i] != 0) count++;

b = malloc(count * sizeof(int));
 int j = 0;

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

if (a[i] != 0) {

b[j++] = a[i];

sum += a[i];

printf("Sum = %d\n", sum);

free(a); free(b);

return 0;

// Q3: Structure for student details

#include <stdio.h>

struct Student {

int roll;

char name[50];

float marks;

};

int main() {

struct Student s;

printf("Enter roll, name and marks: ");

scanf("%d %s %f", &s.roll, s.name, &s.marks);

printf("Roll: %d\nName: %s\nMarks: %.2f\n", s.roll, s.name, s.marks);

return 0;
}

// Q4: Reverse a string

#include <stdio.h>

#include <string.h>

int main() {

char str[100];

printf("Enter string: ");

gets(str);

strrev(str);

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

return 0;

// Q5: Length of string without strlen()

#include <stdio.h>

int main() {

char str[100];

int i = 0;

printf("Enter string: ");

gets(str);

while (str[i] != '\0') i++;

printf("Length = %d\n", i);

return 0;

}
// Q6: Count vowels in string

#include <stdio.h>

int main() {

char str[100];

int i, count = 0;

printf("Enter string: ");

gets(str);

for (i = 0; str[i] != '\0'; i++) {

if (str[i]=='a'||str[i]=='e'||str[i]=='i'||str[i]=='o'||str[i]=='u'||

str[i]=='A'||str[i]=='E'||str[i]=='I'||str[i]=='O'||str[i]=='U') {

count++;

printf("Vowels = %d\n", count);

return 0;

// Q7: Concatenate two strings

#include <stdio.h>

#include <string.h>

int main() {

char a[100], b[100];

gets(a); gets(b);

strcat(a, b);
 printf("Result: %s\n", a);

return 0;

// Q8: Compare two strings

#include <stdio.h>

#include <string.h>

int main() {

char a[100], b[100];

gets(a); gets(b);

if (strcmp(a, b) == 0) printf("Equal\n");

else printf("Not equal\n");

return 0;

// Q9: Copy string

#include <stdio.h>

#include <string.h>

int main() {

char a[100], b[100];

gets(a);

strcpy(b, a);

printf("Copied string: %s\n", b);

return 0;

}
// Q10: Palindrome string

#include <stdio.h>

#include <string.h>

int main() {

char str[100], rev[100];

gets(str);

strcpy(rev, str);

strrev(rev);

if (strcmp(str, rev) == 0) printf("Palindrome\n");

else printf("Not Palindrome\n");

return 0;

// Q1 to Q10 are already above

// Q11: Swap using pointers

#include <stdio.h>

void swap(int *a, int *b) {

int temp = *a;

*a = *b;

*b = temp;

int main() {

int x = 10, y = 20;

swap(&x, &y);
 printf("x=%d y=%d\n", x, y);

return 0;

// Q12: Pointer to pointer

#include <stdio.h>

int main() {

int a = 5, *p, **pp;

p = &a;

pp = &p;

printf("Value: %d\n", **pp);

return 0;

// Q13: Pointer with array

#include <stdio.h>

int main() {

int a[5] = {1,2,3,4,5}, *p = a, i;

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

printf("%d ", *(p+i));

return 0;

// Q14: Factorial using recursion

int fact(int n) {

return (n <= 1) ? 1 : n * fact(n - 1);

int main() {

int n;

scanf("%d", &n);

printf("Factorial = %d\n", fact(n));

return 0;

// Q15: Fibonacci using recursion

#include <stdio.h>

int fib(int n) {

if (n <= 1) return n;

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

int main() {

int n;

scanf("%d", &n);

for (int i = 0; i < n; i++)

printf("%d ", fib(i));

return 0;

}
// Q16: GCD using recursion

#include <stdio.h>

int gcd(int a, int b) {

return b == 0 ? a : gcd(b, a % b);

int main() {

int x, y;

scanf("%d %d", &x, &y);

printf("GCD = %d\n", gcd(x, y));

return 0;

// Q17: Reverse number using recursion

#include <stdio.h>

int rev(int n, int r) {

if (n == 0) return r;

return rev(n/10, r*10 + n%10);

int main() {

int n;

scanf("%d", &n);

printf("Reverse = %d\n", rev(n, 0));

return 0;

}
// Q18: Even or Odd using function

#include <stdio.h>

void check(int n) {

if(n%2 == 0) printf("Even\n");

else printf("Odd\n");

int main() {

int n;

scanf("%d", &n);

check(n);

return 0;

// Q19: Prime check

#include <stdio.h>

int isPrime(int n) {

if (n <= 1) return 0;

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

if (n % i == 0) return 0;

return 1;

int main() {

int n;

scanf("%d", &n);

if (isPrime(n)) printf("Prime\n");
 else printf("Not Prime\n");

return 0;

// Q20: Armstrong number

#include <stdio.h>

int isArmstrong(int n) {

int temp = n, sum = 0;

while (n > 0) {

int d = n % 10;

sum += d * d * d;

n /= 10;

return temp == sum;

int main() {

int n;

scanf("%d", &n);

if (isArmstrong(n)) printf("Armstrong\n");

else printf("Not Armstrong\n");

return 0;

// Q21: Sum of digits

#include <stdio.h>
int sumDigits(int n) {

int sum = 0;

while (n > 0) {

sum += n % 10;

n /= 10;

return sum;

int main() {

int n;

scanf("%d", &n);

printf("Sum = %d\n", sumDigits(n));

return 0;

// Q22: Count digits

#include <stdio.h>

int countDigits(int n) {

int count = 0;

while (n != 0) {

count++;

n /= 10;

return count;

}
int main() {

int n;

scanf("%d", &n);

printf("Digits = %d\n", countDigits(n));

return 0;

// Q23: Swap using function

// (Same as Q11)

// Q24: Sort array ascending

#include <stdio.h>

void sort(int a[], int n) {

for (int i=0; i<n-1; i++)

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

if (a[i] > a[j]) {

int t = a[i]; a[i] = a[j]; a[j] = t;

int main() {

int a[100], n;

scanf("%d", &n);

for (int i = 0; i < n; i++) scanf("%d", &a[i]);

sort(a, n);

for (int i = 0; i < n; i++) printf("%d ", a[i]);

// Q25: Matrix addition

#include <stdio.h>

int main() {

int a[2][2], b[2][2], c[2][2];

for (int i=0;i<2;i++) for (int j=0;j<2;j++) scanf("%d", &a[i][j]);

for (int i=0;i<2;i++) for (int j=0;j<2;j++) scanf("%d", &b[i][j]);

for (int i=0;i<2;i++) for (int j=0;j<2;j++) c[i][j] = a[i][j] + b[i][j];

for (int i=0;i<2;i++) {

for (int j=0;j<2;j++) printf("%d ", c[i][j]);

printf("\n");

return 0;

// Q26: Matrix multiplication

#include <stdio.h>

int main() {

int a[2][2], b[2][2], c[2][2] = {0};

for (int i=0;i<2;i++) for (int j=0;j<2;j++) scanf("%d", &a[i][j]);

for (int i=0;i<2;i++) for (int j=0;j<2;j++) scanf("%d", &b[i][j]);

for (int i=0;i<2;i++)

for (int j=0;j<2;j++)

c[i][j] += a[i][k] * b[k][j];

for (int i=0;i<2;i++) {

for (int j=0;j<2;j++) printf("%d ", c[i][j]);

printf("\n");

return 0;

// Q27: Sum of diagonal

#include <stdio.h>

int main() {

int a[2][2], sum = 0;

for (int i=0;i<2;i++)

for (int j=0;j<2;j++) {

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

if (i == j) sum += a[i][j];

printf("Diagonal sum = %d\n", sum);

return 0;

// Q28: File read/write

#include <stdio.h>

int main() {
 FILE *f = fopen("data.txt", "w");

fprintf(f, "Hello file!\n");

fclose(f);

f = fopen("data.txt", "r");

char ch;

while ((ch = fgetc(f)) != EOF)

putchar(ch);

fclose(f);

return 0;

// Q29: Command line arguments

#include <stdio.h>

int main(int argc, char *argv[]) {

printf("Arg 1 = %s\n", argv[1]);

return 0;