diff --git a/function_array.c b/function_array.c
new file mode 100644
index 0000000..a9fc33a
--- /dev/null
+++ b/function_array.c
@@ -0,0 +1,66 @@
+/**
+ * @file function_array.c
+ * @author kunal jain (kunal.jain001@umb.edu)
+ * @brief Program to demonstrate how functions
+ *        work with arrays as arguments.
+ *        Given an integer array, we will increase 
+ *        all elements of array by one using function.
+ * @version 0.1
+ * @date 2022-02-05
+ * 
+ * @copyright Copyright (c) 2022
+ * 
+ */
+
+#include<stdio.h>
+
+// Function to print array.
+// Parameters - array, length of array.
+// Returns - void
+void printa(int arr[], int len) {
+    int i;
+    for (i = 0; i < len; i++) {
+        printf("%d ", arr[i]);
+    }
+    printf("\n");
+}
+
+// Function to increase all elements in an array by one
+// Parameters - array, length of array
+// Returns - void
+void increase_by_one(int arr[], int len) {
+    int i;
+    for (i = 0; i < len; i++) {
+        arr[i] = arr[i] + 1;
+    }
+}
+
+int main(void) {
+    
+    int i;
+    // Array declared of two values.
+    int arr[2] = {1, 2};
+
+    // Print array before calling function.
+    // printa function expects two arguments - array and length of array
+    printf("Initial array values\n");
+    printa(arr, 2);
+
+    // Function called to increase value
+    // increase_by_one expects one argument - array
+    //
+    // Notice that function is not returning any value.
+    // When array is passed as an argument, the value passed to the 
+    // function is the address of the beginning of the array.
+    // All changes to array in function will be seen here as well.
+    increase_by_one(arr, 2);
+
+    // When array is printed after calling increase_by_one function,
+    // Values of array are incremented even though function did not
+    // return updated array.
+    printf("Final Array values\n");
+    printa(arr, 2);
+
+    return 0;
+
+}
\ No newline at end of file
diff --git a/function_call-by-reference.c b/function_call-by-reference.c
new file mode 100644
index 0000000..fc672c4
--- /dev/null
+++ b/function_call-by-reference.c
@@ -0,0 +1,44 @@
+/**
+ * @file function_call-by-reference.c
+ * @author kunal jain (kunal.jain001@umb.edu)
+ * @brief Program to write a function to swap 2 numbers
+ * @version 0.1
+ * @date 2022-02-02
+ * 
+ * @copyright Copyright (c) 2022
+ * 
+ */
+
+#include<stdio.h>
+
+// Declare and define a function to swap two numbers
+// Pointer variable -> Variable to store address of another variable.
+
+// In this swap function, we will change the value of variable present
+// at the memory location where pointer is pointing.
+void swap (int *x, int *y) {
+
+    int temp;
+    
+    temp = *x;
+    *x = *y;
+    *y = temp;
+
+}
+
+int main(void) {
+    int a = 7, b = 5;
+    
+    printf("%d %d\n", a, b);
+    
+    // Pass address instead of variable.
+
+    // Address of(&) -> Address of operator gives address of
+    //                 the variable. 
+    swap(&a, &b);
+
+    // Values of a and b changes once address is passed as argument.
+    printf("%d %d\n", a, b);
+
+    return 0; 
+}
\ No newline at end of file
diff --git a/function_char_longest-line.c b/function_char_longest-line.c
new file mode 100644
index 0000000..0fd97d7
--- /dev/null
+++ b/function_char_longest-line.c
@@ -0,0 +1,137 @@
+/**
+ * @file function_char_longest-line.c
+ * @author kunal jain (kunal.jain001@umb.edu)
+ * @brief Program to read input line by line and 
+ *        return longest line from the input.
+ * This program uses functions, character I/O, 
+ * and arrays that we learnt in past classes. This
+ * single program sums it up all.
+ * Assume maximum length of any line in input is 1000 characters.
+ * @version 0.1
+ * @date 2022-02-05
+ * 
+ * @copyright Copyright (c) 2022
+ * 
+ */
+
+// while (there is another line)
+//     if (it's longer than the previous longest)
+//         save it
+//         save its length
+// print longest line
+
+#include<stdio.h>
+
+// Function to read input till new line character and 
+// get length of line.
+// Paramters - char array to store characters that are being read.
+// Return - length of a line as integer
+int getlinelength(char input[]) {
+    // Read a character till new line or EOF.
+
+    // If first character is new line then length of line = 1
+
+    // Put null ('\0') character at the end of the array
+    // to mark end of string of character.
+
+    // Because length of line = number of characters read,
+    // return i
+
+    int character, i;
+
+    // There are two test conditions with AND operator. 
+    // Loop will stop if any one of the condition is false.
+    //
+    // Any changes in char input[] means changes in char line[],
+    // because array passed is pointer to its beginning location.
+    for (i = 0; (character = getchar()) != EOF && character != '\n'; ++i) {
+        input[i] = character;
+    }
+
+    // Added new line character in the end of line as 
+    // line with only new line character has length of one.
+    if (character == '\n') {
+        input[i] = character;
+        ++i;
+    }
+
+    // Put character '\0' (null character) at the end of the array
+    // to mark the end of the string of characters. 
+    input[i] = '\0';
+    
+    // Return length of line which is also equal to number
+    // of characters read
+    return i;
+}
+
+// Function to copy characters from one char array to another
+// This copies 'from' into 'to'.
+// Parameter - char from[], char to[]
+// Return - void
+void copy(char from[], char to[]) {
+
+    int i = 0;
+    
+    // Copy 'from' into 'to' one character at a time
+    // until null character encountered.
+    while ((to[i] = from[i]) != '\0') {
+        i++;
+    }
+    // Any changes in 'to' array means changes in longestline array.
+
+    // This function does not return anything.
+    // Such functions have "void" return type.
+}
+
+int main(void) {
+    
+    // Variable declarations
+
+    // Variable len to hold length of each line.
+    // Variable max to hold length of max line length.
+    int len, max = 0;
+
+    // Character array to store line from input.
+    char line[1000];
+
+    // Character array to store longest line.
+    // We will copy char array line into char array 
+    // longestline if lenght of line is greater 
+    // than current max length.
+    char longestline[1000];
+
+    // Get length of each line using getlinelength function
+        while ((len = getlinelength(line)) > 0) {
+            // If length of line greater than current max length
+            // then update max variable and copy line into
+            // longestline.
+            if (len > max) {
+                max = len;
+                copy(line, longestline);
+            }
+        }
+
+    // If max length of any line read is greater than zero 
+    // then print longestline.
+    if (max > 0) {
+
+        printf("Longest line in the input is -> ");
+        // Two ways to print string in C.
+        
+        // First way - using loop
+        
+        // int i;
+        // for (i = 0; i < max; i++) {
+        //     printf("%c", longestline[i]);
+        // }
+
+        // Second way
+
+        // %s -> Format specifier to print sequence of characters
+        printf("%s", longestline);
+        
+        printf("\n");
+    }
+
+    return 0;
+}