backup

24 files changed, 1216 insertions, 0 deletions

diff --git a/assignments/01-grading-system.c b/assignments/01-grading-system.c
new file mode 100644
index 0000000..3c15f24
--- /dev/null
+++ b/assignments/01-grading-system.c
@@ -0,0 +1,63 @@
+/* Grading system */
+#include <stdio.h>
+
+int main(void)
+{
+	int n1, n2, n3, n4;
+	float avg;
+	printf("Grading system\n\n");
+	printf("Enter marks obtained in four subjects: ");
+	scanf("%d%d%d%d", &n1, &n2, &n3, &n4);
+	avg = (float)(n1 + n2 + n3 + n4)/4;
+	printf("The average of the marks is %f\n", avg);
+	if (avg >= 80)
+		printf("The student has grade A.\n");
+	if (avg >= 60 && avg < 80)
+		printf("The student has grade B.\n");
+	if (avg >= 40 && avg < 60)
+		printf("The student has grade C.\n");
+	if (avg < 40)
+		printf("The student has failed.\n");
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Grading system
+
+Enter marks obtained in four subjects: 81
+85
+86
+91
+The average of the marks is 85.750000
+The student has grade A.
+
+Set 2:
+Grading system
+
+Enter marks obtained in four subjects: 86 75 71 42
+The average of the marks is 68.500000
+The student has grade B.
+
+Set 3:
+Grading system
+
+Enter marks obtained in four subjects: 45
+55
+51
+42
+The average of the marks is 48.250000
+The student has grade C.
+
+Set 4:
+Grading system
+
+Enter marks obtained in four subjects: 25
+31
+40 32
+The average of the marks is 32.000000
+The student has failed.
+
+*/
+
diff --git a/assignments/02-leapyear.c b/assignments/02-leapyear.c
new file mode 100644
index 0000000..f281dc2
--- /dev/null
+++ b/assignments/02-leapyear.c
@@ -0,0 +1,47 @@
+/* Leap year */
+#include <stdio.h>
+
+int main(void)
+{
+	int year;
+	printf("Enter a year: ");
+	scanf("%d", &year);
+	if (year <= 1200 || year >= 9999) {
+		printf("Invalid year.\n");
+		return 0;
+	}
+	if ((year % 400 == 0) || (year % 100 != 0 && year % 4 == 0))
+		printf("%d is a leap year.\n", year);
+	else
+		printf("%d is not a leap year.\n", year);
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Enter a year: 1300
+1300 is not a leap year.
+
+Set 2:
+Enter a year: 1600
+1600 is a leap year.
+
+Set 3:
+Enter a year: 2008
+2008 is a leap year.
+
+Set 4:
+Enter a year: 2003
+2003 is not a leap year.
+
+Set 5:
+Enter a year: 1100
+Invalid year.
+
+Set 6:
+Enter a year: 10000
+Invalid year.
+
+*/
+
diff --git a/assignments/03-quadratic-equation.c b/assignments/03-quadratic-equation.c
new file mode 100644
index 0000000..d7000df
--- /dev/null
+++ b/assignments/03-quadratic-equation.c
@@ -0,0 +1,79 @@
+/* Quadratic equation and the nature of the roots */
+
+#include <stdio.h>
+#include <math.h>
+
+int main(void)
+{
+	float a, b, c, discr, x1, x2;
+	printf("Finding the roots and the nature of them of quadratic equation\n"
+		"\t\tax^2+bx+c=0\n\n");
+	printf("Enter a: ");
+	scanf("%f", &a);
+	printf("Enter b: ");
+	scanf("%f", &b);
+	printf("Enter c: ");
+	scanf("%f", &c);
+	if (a == 0) {
+		printf("In a quadratic equation, a can not be zero.\n");
+		return 0;
+	}
+	discr = b * b - 4 * a * c;
+	if (discr < 0) {
+		printf("The roots of this equation are imaginary.\n");
+		return 0;
+	}
+	if (discr == 0) {
+		printf("The roots of this equation are real and equal.\n");
+	}
+	if (discr > 0) {
+		printf("The roots of this equation are real and distinct.\n");
+	}
+	x1 = (-b + sqrt(discr)) / (2 * a);
+	x2 = (-b - sqrt(discr)) / (2 * a);
+	printf("The roots are: %f and %f\n", x1, x2);
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Finding the roots and the nature of them of quadratic equation
+		ax^2+bx+c=0
+
+Enter a: 0
+Enter b: -1
+Enter c: 2
+In a quadratic equation, a can not be zero.
+
+Set 2:
+Finding the roots and the nature of them of quadratic equation
+		ax^2+bx+c=0
+
+Enter a: -1
+Enter b: 4
+Enter c: -5
+The roots of this equation are imaginary.
+
+Set 3:
+Finding the roots and the nature of them of quadratic equation
+		ax^2+bx+c=0
+
+Enter a: 2.5
+Enter b: -5
+Enter c: 2.5
+The roots of this equation are real and equal.
+The roots are: 1.000000 and 1.000000
+
+Set 4:
+Finding the roots and the nature of them of quadratic equation
+		ax^2+bx+c=0
+
+Enter a: -1.23
+Enter b: 45.6
+Enter c: 789
+The roots of this equation are real and distinct.
+The roots are: -12.849214 and 49.922382
+
+*/
+
diff --git a/assignments/04-sum-product-of-digits.c b/assignments/04-sum-product-of-digits.c
new file mode 100644
index 0000000..d49acd3
--- /dev/null
+++ b/assignments/04-sum-product-of-digits.c
@@ -0,0 +1,49 @@
+/* Sum and product of the digits of given number */
+
+#include <stdio.h>
+
+int main(void)
+{
+	int n, m, r, sum, prod;
+	printf("Sum and product of the digits of a given number\n\n");
+	printf("Enter a number: ");
+	scanf("%d", &n);
+	m = n;
+	sum = 0;
+	prod = 1;
+	do {
+		r = m % 10;
+		m = m / 10;
+		sum = sum + r;
+		prod = prod * r;
+	} while (m > 0);
+	printf("Sum of digits of %d is %d\n", n, sum);
+	printf("Product of digits of %d is %d\n", n, prod);
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Sum and product of the digits of a given number
+
+Enter a number: 0
+Sum of digits of 0 is 0
+Product of digits of 0 is 0
+
+Set 2:
+Sum and product of the digits of a given number
+
+Enter a number: 123456
+Sum of digits of 123456 is 21
+Product of digits of 123456 is 720
+
+Set 3:
+Sum and product of the digits of a given number
+
+Enter a number: 123456789
+Sum of digits of 123456789 is 45
+Product of digits of 123456789 is 362880
+
+*/
+
diff --git a/assignments/05-reverse-digits.c b/assignments/05-reverse-digits.c
new file mode 100644
index 0000000..05fadd7
--- /dev/null
+++ b/assignments/05-reverse-digits.c
@@ -0,0 +1,43 @@
+/* Print the digits of given number in reverse order */
+
+#include <stdio.h>
+
+int main(void)
+{
+	int n, m, r, sum, prod;
+	printf("Print the digits of given number in reverse order\n\n");
+	printf("Enter a number: ");
+	scanf("%d", &n);
+	m = n;
+	printf("%d printed in reverse order is: ", n);
+	do {
+		r = m % 10;
+		m = m / 10;
+		printf("%d", r);
+	} while (m > 0);
+	printf("\n");
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Print the digits of given number in reverse order
+
+Enter a number: 0
+0 printed in reverse order is: 0
+
+Set 2:
+Print the digits of given number in reverse order
+
+Enter a number: 123456
+123456 printed in reverse order is: 654321
+
+Set 3:
+Print the digits of given number in reverse order
+
+Enter a number: 541563249
+541563249 printed in reverse order is: 942365145
+
+*/
+
diff --git a/assignments/06-check-palindrome-number.c b/assignments/06-check-palindrome-number.c
new file mode 100644
index 0000000..d1a10d8
--- /dev/null
+++ b/assignments/06-check-palindrome-number.c
@@ -0,0 +1,47 @@
+/* Check whether a given number is palindromic or not */
+
+#include <stdio.h>
+
+int main(void)
+{
+	int n, m, p, r;
+	printf("Check whether a given number is palindromic\n\n");
+	printf("Enter a number: ");
+	scanf("%d", &n);
+	m = n;
+	p = 0;
+	while (m > 0) {
+		r = m % 10;
+		m = m / 10;
+		p = p * 10 + r;
+	}
+	if (p == n) {
+		printf("%d is a palindromic number.\n", n);
+	} else {
+		printf("%d is not a palindromic number.\n", n);
+	}
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Check whether a given number is palindromic
+
+Enter a number: 0
+0 is a palindromic number.
+
+Set 2:
+Check whether a given number is palindromic
+
+Enter a number: 123456
+123456 is not a palindromic number.
+
+Set 3:
+Check whether a given number is palindromic
+
+Enter a number: 1234321
+1234321 is a palindromic number.
+
+*/
+
diff --git a/assignments/07-check-prime.c b/assignments/07-check-prime.c
new file mode 100644
index 0000000..3a492ef
--- /dev/null
+++ b/assignments/07-check-prime.c
@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+bool is_prime(int n)
+{
+	int i;
+	for (i = 2; i < n; i++) {
+		if (n % i == 0) return false;
+	}
+	return true;
+}
+
+int main(void)
+{
+	int i, n;
+	printf("Check whether a given number is prime or not\n\n");
+	printf("Enter a number: ");
+	scanf("%d", &n);
+	if (n < 2) {
+		printf("Invalid input, it must be an integer greater than 2\n");
+		return 0;
+	}
+	printf("%d is%s a prime number.\n", n, is_prime(n) ? "" : " not");
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Check whether a given number is prime or not
+
+Enter a number: 100
+100 is not a prime number.
+
+Set 2:
+Check whether a given number is prime or not
+
+Enter a number: 97
+97 is a prime number.
+
+Set 3:
+Check whether a given number is prime or not
+
+Enter a number: 2
+2 is a prime number.
+
+Set 4:
+Check whether a given number is prime or not
+
+Enter a number: 1
+Invalid input, it must be an integer greater than 2
+
+
+*/
+
diff --git a/assignments/08-prime-factors.c b/assignments/08-prime-factors.c
new file mode 100644
index 0000000..93b027d
--- /dev/null
+++ b/assignments/08-prime-factors.c
@@ -0,0 +1,46 @@
+/* Print the prime factorization of a given number */
+
+#include <stdio.h>
+
+int main(void)
+{
+	int n, m, i;
+	printf("Print the prime factorization of a given number\n\n");
+	printf("Enter a number: ");
+	scanf("%d", &n);
+	printf("The prime factors of %d are: ", n);
+	m = n;
+	while (m > 1) {
+		for (i = 2; i <= m; i++) {
+			while (m % i == 0) {
+				printf("%d ", i);
+				m = m / i;
+			}
+		}
+	}
+	printf("\n");
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Print the prime factorization of a given number
+
+Enter a number: 2
+The prime factors of 2 are: 2 
+
+Set 2:
+Print the prime factorization of a given number
+
+Enter a number: 120
+The prime factors of 120 are: 2 2 2 3 5 
+
+Set 3:
+Print the prime factorization of a given number
+
+Enter a number: 97
+The prime factors of 97 are: 97 
+
+*/
+
diff --git a/assignments/09-check-perfect-number.c b/assignments/09-check-perfect-number.c
new file mode 100644
index 0000000..33b575e
--- /dev/null
+++ b/assignments/09-check-perfect-number.c
@@ -0,0 +1,53 @@
+/* Check whether a given number is a perfect number */
+
+#include <stdio.h>
+
+int main(void)
+{
+	int n, sum, i, j, isprime;
+	printf("Check whether a given number is a perfect number\n\n");
+	printf("Enter a number: ");
+	scanf("%d", &n);
+	sum = 0;
+	for (i = 1; i < n; i++) {
+		if (n % i == 0) {
+			sum += i;
+		}
+	}
+	if (n == sum) {
+		printf("%d is a perfect number.\n", n);
+	} else {
+		printf("%d is not a perfect number.\n", n);
+	}
+	return 0;
+}
+
+
+/*
+Output:
+Set 1:
+Check whether a given number is a perfect number
+
+Enter a number: 6
+6 is a perfect number.
+
+Set 2:
+Check whether a given number is a perfect number
+
+Enter a number: 10
+10 is not a perfect number.
+
+Set 3:
+Check whether a given number is a perfect number
+
+Enter a number: 28
+28 is a perfect number.
+
+Set 4:
+Check whether a given number is a perfect number
+
+Enter a number: 100
+100 is not a perfect number.
+
+*/
+
diff --git a/assignments/10-hcf-lcm.c b/assignments/10-hcf-lcm.c
new file mode 100644
index 0000000..4a10e3d
--- /dev/null
+++ b/assignments/10-hcf-lcm.c
@@ -0,0 +1,54 @@
+/* Calculate the highest common factor and lowest common multiplier of two numbers */
+
+#include <stdio.h>
+
+int main(void)
+{
+	int a, b, m, n, t;
+	printf("Calculate the HCF and LCM of two numbers\n\n");
+	printf("Enter two numbers: ");
+	scanf("%d%d", &a, &b);
+	m = a;
+	n = b;
+	while (n > 0) {
+		t = n;
+		n = m % n;
+		m = t;
+	}
+	printf("The HCF of %d and %d is %d\n", a, b, m);
+	printf("The LCM of %d and %d is %d\n", a, b, (a*b)/m);
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Calculate the HCF and LCM of two numbers
+
+Enter two numbers: 12 16
+The HCF of 12 and 16 is 4
+The LCM of 12 and 16 is 48
+
+Set 2:
+Calculate the HCF and LCM of two numbers
+
+Enter two numbers: 112 67
+The HCF of 112 and 67 is 1
+The LCM of 112 and 67 is 7504
+
+Set 3:
+Calculate the HCF and LCM of two numbers
+
+Enter two numbers: 1 2
+The HCF of 1 and 2 is 1
+The LCM of 1 and 2 is 2
+
+Set 4:
+Calculate the HCF and LCM of two numbers
+
+Enter two numbers: 123 456
+The HCF of 123 and 456 is 3
+The LCM of 123 and 456 is 18696
+
+*/
+
diff --git a/assignments/11-fibonacci.c b/assignments/11-fibonacci.c
new file mode 100644
index 0000000..4019a7c
--- /dev/null
+++ b/assignments/11-fibonacci.c
@@ -0,0 +1,44 @@
+/* Print first n fibonacci numbers */
+
+#include <stdio.h>
+
+int main(void)
+{
+	int a, b, i, n, t;
+	printf("Print first n fibonacci number\n\n");
+	printf("Enter a number: ");
+	scanf("%d", &n);
+	a = 1; b = 0;
+	printf("The first %d fibonacci numbers are: ", n);
+	for (i = 1; i <= n; i++) {
+		printf("%d ", b);
+		t = a;
+		a = a + b;
+		b = t;
+	}
+	printf("\n");
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Print first n fibonacci number
+
+Enter a number: 5
+The first 5 fibonacci numbers are: 0 1 1 2 3 
+
+Set 2:
+Print first n fibonacci number
+
+Enter a number: 10
+The first 10 fibonacci numbers are: 0 1 1 2 3 5 8 13 21 34 
+
+Set 3:
+Print first n fibonacci number
+
+Enter a number: 20
+The first 20 fibonacci numbers are: 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 
+
+*/
+
diff --git a/assignments/12-armstrong-range.c b/assignments/12-armstrong-range.c
new file mode 100644
index 0000000..cc57fb4
--- /dev/null
+++ b/assignments/12-armstrong-range.c
@@ -0,0 +1,62 @@
+#include <math.h>
+#include <stdio.h>
+#include <stdbool.h>
+
+bool is_armstrong(int n)
+{
+	int m = n, r, s = 0;
+	float c = ceil(log10(n));
+	while (m > 0) {
+		r = m % 10;
+		m /= 10;
+		s += pow(r, c);
+	}
+	return n == s;
+}
+
+int main(void)
+{
+	int i, l, h;
+	printf("Print Armstrong Numbers in a given range\n\n");
+	printf("Enter the range: ");
+	scanf("%d%d", &l, &h);
+	if (h < l) {
+		printf("Invalid range\n");
+		return 0;
+	}
+	printf("Armstrong numbers between %d and %d are: ", l, h);
+	for (i = l; i <= h; i++) {
+		if (is_armstrong(i)) printf("%d ", i);
+	}
+	printf("\n");
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Print Armstrong Numbers in a given range
+
+Enter the range: 100 1
+Invalid range
+
+Set 2:
+Print Armstrong Numbers in a given range
+
+Enter the range: 1 100
+Armstrong numbers between 1 and 100 are: 1 2 3 4 5 6 7 8 9 
+
+Set 3:
+Print Armstrong Numbers in a given range
+
+Enter the range: 100 10000
+Armstrong numbers between 100 and 10000 are: 153 370 371 407 1634 8208 9474 
+
+Set 4:
+Print Armstrong Numbers in a given range
+
+Enter the range: 10000 1000000
+Armstrong numbers between 10000 and 1000000 are: 54748 92727 93084 548834 
+
+*/
+
diff --git a/assignments/13-binary-pattern.c b/assignments/13-binary-pattern.c
new file mode 100644
index 0000000..5b3e4a9
--- /dev/null
+++ b/assignments/13-binary-pattern.c
@@ -0,0 +1,65 @@
+#include <stdio.h>
+
+int main(void)
+{
+	int i, j, h, f;
+	printf("Enter a height: ");
+	scanf("%d", &h);
+	for (i = 1; i <= h; i++) {
+		f = i % 2;
+		for (j = 1; j <= i; j++) {
+			printf("%d", f);
+			f = !f;
+		}
+		printf("\n");
+	}
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Enter a height: 5
+1
+01
+101
+0101
+10101
+
+Set 2:
+Enter a height: 6
+1
+01
+101
+0101
+10101
+010101
+
+Set 3:
+Enter a height: 8
+1
+01
+101
+0101
+10101
+010101
+1010101
+01010101
+
+Set 4:
+Enter a height: 11
+1
+01
+101
+0101
+10101
+010101
+1010101
+01010101
+101010101
+0101010101
+10101010101
+
+
+*/
+
diff --git a/assignments/14-star-pattern-90t.c b/assignments/14-star-pattern-90t.c
new file mode 100644
index 0000000..2a285d2
--- /dev/null
+++ b/assignments/14-star-pattern-90t.c
@@ -0,0 +1,47 @@
+#include <stdio.h>
+
+int main(void)
+{
+	int i, j, h;
+	printf("Enter a height: ");
+	scanf("%d", &h);
+	for (i = 1; i <= h; i++) {
+		for (j = 1; j <= 2 * (h - i); j++) {
+			printf(" ");
+		}
+		for (j = 1; j <= 2 * i - 1; j++) {
+			printf("*");
+		}
+		printf("\n");
+	}
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Enter a height: 3
+    *
+  ***
+*****
+
+Set 2:
+Enter a height: 5
+        *
+      ***
+    *****
+  *******
+*********
+
+Set 3:
+Enter a height: 7
+            *
+          ***
+        *****
+      *******
+    *********
+  ***********
+*************
+
+*/
+
diff --git a/assignments/15-star-pattern-eql.c b/assignments/15-star-pattern-eql.c
new file mode 100644
index 0000000..e32b745
--- /dev/null
+++ b/assignments/15-star-pattern-eql.c
@@ -0,0 +1,47 @@
+#include <stdio.h>
+
+int main(void)
+{
+	int i, j, h;
+	printf("Enter a height: ");
+	scanf("%d", &h);
+	for (i = 1; i <= h; i++) {
+		for (j = 1; j <= h - i; j++) {
+			printf(" ");
+		}
+		for (j = 1; j <= 2 * i - 1; j++) {
+			printf("*");
+		}
+		printf("\n");
+	}
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Enter a height: 3
+  *
+ ***
+*****
+
+Set 2:
+Enter a height: 5
+    *
+   ***
+  *****
+ *******
+*********
+
+Set 3:
+Enter a height: 7
+      *
+     ***
+    *****
+   *******
+  *********
+ ***********
+*************
+
+*/
+
diff --git a/assignments/16-star-pattern-extreme.c b/assignments/16-star-pattern-extreme.c
new file mode 100644
index 0000000..97d4d8d
--- /dev/null
+++ b/assignments/16-star-pattern-extreme.c
@@ -0,0 +1,50 @@
+#include <stdio.h>
+
+int main(void)
+{
+	int i, j, h;
+	printf("Enter a height: ");
+	scanf("%d", &h);
+	for (i = 1; i <= h; i++) {
+		for (j = 1; j <= i; j++) {
+			printf("*");
+		}
+		for (j = 1; j <= 2 * h - 2 * i; j++) {
+			printf(" ");
+		}
+		for (j = 1; j <= i; j++) {
+			printf("*");
+		}
+		printf("\n");
+	}
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Enter a height: 4
+*      *
+**    **
+***  ***
+********
+
+Set 2:
+Enter a height: 5
+*        *
+**      **
+***    ***
+****  ****
+**********
+
+Set 3:
+Enter a height: 6
+*          *
+**        **
+***      ***
+****    ****
+*****  *****
+************
+
+*/
+
diff --git a/assignments/17-pascal-triangle.c b/assignments/17-pascal-triangle.c
new file mode 100644
index 0000000..24047c6
--- /dev/null
+++ b/assignments/17-pascal-triangle.c
@@ -0,0 +1,52 @@
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static int count_digits(double n)
+{
+	return floor(log10(n)) + 1;
+}
+
+static double factorial(double n)
+{
+	return tgamma(n + 1);	
+}
+
+static double comb(long n, long r)
+{
+	return factorial(n) / (factorial(r) * factorial(n - r));
+}
+
+int main(void)
+{
+	int i, j, k, h, l, *arr, *p;
+	size_t n;
+	printf("To Print the Pascal's Triangle\n\n");
+	printf("Enter a height: ");
+	scanf("%d", &h);
+	l = count_digits(comb(h, h / 2));
+	arr = malloc((h + 3) * sizeof(int));
+	if (arr == NULL) {
+		printf("Insufficient memory.\n");
+		return 0;
+	}
+	arr[0] = 1;
+	arr[1] = 0;
+	n = 1;
+	for (i = 1; i <= h + 1; i++) {
+		for (k = 1; k <= (h - i + 1) * l; k++) {
+			printf(" ");
+		}
+		for (k = 0; k < n; k++) {
+			printf("%- *d ", l + 1, arr[k]);
+		}
+		printf("\n");
+		arr[k+1] = 0;
+		for (n++; k > 0; k--) {
+			arr[k] += arr[k-1];
+		}
+	}
+	free(arr);
+	return 0;
+}
+
diff --git a/assignments/18-harmonic-series.c b/assignments/18-harmonic-series.c
new file mode 100644
index 0000000..4fc62b1
--- /dev/null
+++ b/assignments/18-harmonic-series.c
@@ -0,0 +1,45 @@
+#include <stdio.h>
+
+int main(void)
+{
+	int i, n;
+	float sum;
+	printf("Calculate the sum of 1/i from i to a given number.\n\n");
+	printf("Enter a number: ");
+	scanf("%d", &n);
+	sum = 0;
+	for (i = 1; i <= n; i++) {
+		sum += 1/(float)i;
+	}
+	printf("The sum is %f\n", sum);
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Calculate the sum of 1/i from i to a given number.
+
+Enter a number: 1
+The sum is 1.000000
+
+Set 2:
+Calculate the sum of 1/i from i to a given number.
+
+Enter a number: 2
+The sum is 1.500000
+
+Set 3:
+Calculate the sum of 1/i from i to a given number.
+
+Enter a number: 10
+The sum is 2.928968
+
+Set 4:
+Calculate the sum of 1/i from i to a given number.
+
+Enter a number: 100
+The sum is 5.187378
+
+*/
+
diff --git a/assignments/19-int-series.c b/assignments/19-int-series.c
new file mode 100644
index 0000000..7403517
--- /dev/null
+++ b/assignments/19-int-series.c
@@ -0,0 +1,46 @@
+#include <stdio.h>
+
+int main(void)
+{
+	int i, sum, n, a;
+	printf("Calculate the sum of (-1)^(n+1) * i for i from 1 to given number.\n\n");
+	printf("Enter a number: ");
+	scanf("%d", &n);
+	a = 1;
+	sum = 0;
+	for (i = 1; i <= n; i++) {
+		sum += a * i;
+		a = -a;
+	}
+	printf("The sum is %d\n", sum);
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+Calculate the sum of (-1)^(n+1) * i for i from 1 to given number.
+
+Enter a number: 1
+The sum is 1
+
+Set 2:
+Calculate the sum of (-1)^(n+1) * i for i from 1 to given number.
+
+Enter a number: 2
+The sum is -1
+
+Set 3:
+Calculate the sum of (-1)^(n+1) * i for i from 1 to given number.
+
+Enter a number: 10
+The sum is -5
+
+Set 4:
+Calculate the sum of (-1)^(n+1) * i for i from 1 to given number.
+
+Enter a number: 123
+The sum is 62
+
+*/
+
diff --git a/assignments/20-exp.c b/assignments/20-exp.c
new file mode 100644
index 0000000..b9a4721
--- /dev/null
+++ b/assignments/20-exp.c
@@ -0,0 +1,54 @@
+#include <stdio.h>
+
+#define STEPS 100
+
+double my_exp(double x)
+{
+	int i;
+	double n = 1;
+	double p = 1;
+	for (i = 1; i <= STEPS; i++) {
+		p *= x / i;
+		n += p;
+	}
+	return n;
+}
+
+int main(void)
+{
+	double x;
+	printf("To calculate exp(x) for a given number x\n\n");
+	printf("Enter a number: ");
+	scanf("%lf", &x);
+	printf("exp(%.14g) = %.14g\n", x, my_exp(x));
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+To calculate exp(x) for a given number x
+
+Enter a number: 1
+exp(1) = 2.718281828459
+
+Set 2:
+To calculate exp(x) for a given number x
+
+Enter a number: 2
+exp(2) = 7.3890560989306
+
+Set 3:
+To calculate exp(x) for a given number x
+
+Enter a number: 0.1 
+exp(0.1) = 1.1051709180756
+
+Set 4:
+To calculate exp(x) for a given number x
+
+Enter a number: -1
+exp(-1) = 0.36787944117144
+
+*/
+
diff --git a/assignments/21-sin-cos.c b/assignments/21-sin-cos.c
new file mode 100644
index 0000000..c8b2896
--- /dev/null
+++ b/assignments/21-sin-cos.c
@@ -0,0 +1,71 @@
+#include <stdio.h>
+
+#define STEPS 1000
+
+double my_sin(double x)
+{
+	int i;
+	double n = x;
+	double p = x;
+	for (i = 2; i <= STEPS * 2; i += 2) {
+		p *= -1 * x * x / (i * (i + 1));
+		n += p;
+	}
+	return n;
+}
+
+double my_cos(double x)
+{
+	int i;
+	double n = 1;
+	double p = 1;
+	for (i = 2; i <= STEPS * 2; i += 2) {
+		p *= -1 * x * x / (i * (i - 1));
+		n += p;
+	}
+	return n;
+}
+
+int main(void)
+{
+	double x;
+	printf("To calculate the sine and cosine of a given number\n\n");
+	printf("Enter a number: ");
+	scanf("%lf", &x);
+	printf("sin(%.14g) = %.14g\n", x, my_sin(x));
+	printf("cos(%.14g) = %.14g\n", x, my_cos(x));
+	return 0;
+}
+
+/*
+Output:
+Set 1:
+To calculate the sine and cosine of a given number
+
+Enter a number: 0
+sin(0) = 0
+cos(0) = 1
+
+Set 2:
+To calculate the sine and cosine of a given number
+
+Enter a number: 1.5707963267948966
+sin(1.5707963267949) = 1
+cos(1.5707963267949) = 4.2647940513479e-17
+
+Set 3:
+To calculate the sine and cosine of a given number
+
+Enter a number: 3.141592653579893
+sin(3.1415926535799) = 9.9005553937036e-12
+cos(3.1415926535799) = -1
+
+Set 4:
+To calculate the sine and cosine of a given number
+
+Enter a number: -0.13720941543579
+sin(-0.13720941543579) = -0.13677929342038
+cos(-0.13720941543579) = 0.99060154698618
+
+*/
+
diff --git a/assignments/22-dec-to-roman.c b/assignments/22-dec-to-roman.c
new file mode 100644
index 0000000..05a9553
--- /dev/null
+++ b/assignments/22-dec-to-roman.c
@@ -0,0 +1,53 @@
+#include <stdio.h>
+
+void roman_part(int n, int l, char u, char h, char p)
+{
+	int i, k; 
+	if (n >= l) {
+		k = n / l;
+		if (k == 9) {
+			printf("%c%c", u, p);
+		} else if (k >= 5) {
+			printf("%c", h);
+			for (i = 6; i <= k; i++) {
+				printf("%c", u);
+			}
+		} else if (k == 4) {
+			printf("%c%c", u, h);
+		} else {
+			for (i = 1; i <= k; i++) {
+				printf("%c", u);
+			}
+		}
+	}
+}
+
+void decimal_to_roman(int n)
+{
+	int i, k;
+	if (n >= 1000) {
+		k = n / 1000;
+		for (i = 1; i <= k; i++) {
+			printf("M");
+		} 
+	}
+	roman_part(n % 1000, 100, 'C', 'D', 'M');
+	roman_part(n % 100, 10, 'X', 'L', 'C');
+	roman_part(n % 10, 1, 'I', 'V', 'X');
+	printf("\n");
+}
+
+int main(void)
+{
+	int n;
+	printf("To convert a decimal number to roman number\n\n");
+	printf("Enter a number: ");
+	scanf("%d", &n);
+	if (n < 1 || n > 3999) {
+		printf("Invalid input: it must be between 1 and 3999, inclusive.\n");
+		return 0;
+	}
+	decimal_to_roman(n);
+	return 0;
+}
+
diff --git a/assignments/23-basic-calculator.c b/assignments/23-basic-calculator.c
new file mode 100644
index 0000000..203fdf8
--- /dev/null
+++ b/assignments/23-basic-calculator.c
@@ -0,0 +1,23 @@
+#include <stdio.h>
+
+int menu_option(char *choice)
+{
+	printf(
+	"Basic Calculator\n"
+	"================\n"
+	"Menu:\n"
+	"	+  Add\n"
+	"	-  Subtract\n"
+	"	*  Multiply\n"
+	"	/  Divide\n"
+	"	q  Quit\n\n"
+	);
+}
+
+int main(void)
+{
+	char *choice;
+	menu_option(&choice);
+	return 0;
+}
+
diff --git a/assignments/24-value-vs-ref.c b/assignments/24-value-vs-ref.c
new file mode 100644
index 0000000..8640792
--- /dev/null
+++ b/assignments/24-value-vs-ref.c
@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+void swap_by_value(int a, int b)
+{
+	int c = a;
+	b = a;
+	b = c;
+}
+
+void swap_by_ref(int *a, int *b)
+{
+	int c = *a;
+	*a = *b;
+	*b = c;
+}
+
+int main(void)
+{
+	return 0;
+}
+