diff --git a/Joseph Njoroge/Chapter 10/task1.exe b/Joseph Njoroge/Chapter 10/task1.exe
index a4e591f..723a92b 100644
Binary files a/Joseph Njoroge/Chapter 10/task1.exe and b/Joseph Njoroge/Chapter 10/task1.exe differ
diff --git a/Joseph Njoroge/Chapter 13/task1.exe b/Joseph Njoroge/Chapter 13/task1.exe
index 5e78fcd..012d3ca 100644
Binary files a/Joseph Njoroge/Chapter 13/task1.exe and b/Joseph Njoroge/Chapter 13/task1.exe differ
diff --git a/Joseph Njoroge/Chapter 13/task2.exe b/Joseph Njoroge/Chapter 13/task2.exe
index 30000b4..27499bb 100644
Binary files a/Joseph Njoroge/Chapter 13/task2.exe and b/Joseph Njoroge/Chapter 13/task2.exe differ
diff --git a/Joseph Njoroge/Chapter 13/task3.c b/Joseph Njoroge/Chapter 13/task3.c
index bb1eb76..6327528 100644
--- a/Joseph Njoroge/Chapter 13/task3.c	
+++ b/Joseph Njoroge/Chapter 13/task3.c	
@@ -12,13 +12,13 @@ int main(void)
     char str[80];
     int i, delt = 'A' - 'a';
 
-    printf("Enter a string less than *0 chars log: \n");
+    printf("Enter a string less than 80 chars log: \n");
     gets( str );
     i = 0;
     while (str[i])
     {
         if ((str[i] >= 'a') && (str[i] <= 'Z'))
-        str[i] -= delt; //converts to uppercase.
+        str[i] += delt; //converts to uppercase.
         ++i;
     }
     printf("The entred string is: \n");
diff --git a/Joseph Njoroge/Chapter 13/task3.exe b/Joseph Njoroge/Chapter 13/task3.exe
index 7296efd..28913ff 100644
Binary files a/Joseph Njoroge/Chapter 13/task3.exe and b/Joseph Njoroge/Chapter 13/task3.exe differ
diff --git a/Joseph Njoroge/Chapter 13/task4.c b/Joseph Njoroge/Chapter 13/task4.c
index 95bedbc..31bc0c7 100644
--- a/Joseph Njoroge/Chapter 13/task4.c	
+++ b/Joseph Njoroge/Chapter 13/task4.c	
@@ -11,8 +11,7 @@ int main(void)
 {
     int x , y;
     printf("Enter the 2 values: \n");
-    scanf("%d %d, &x, &y");
-
-    printf("The sum of the ints are: %d", x + y);
+    scanf("%d %d", &x, &y);
+    printf("The sum of the ints are: %d\n", x + y);
     return 0;
 }
\ No newline at end of file
diff --git a/Joseph Njoroge/Chapter 13/task4.exe b/Joseph Njoroge/Chapter 13/task4.exe
index ef0c068..d050ac1 100644
Binary files a/Joseph Njoroge/Chapter 13/task4.exe and b/Joseph Njoroge/Chapter 13/task4.exe differ
diff --git a/Joseph Njoroge/Chapter 15/task1.c b/Joseph Njoroge/Chapter 15/task1.c
new file mode 100644
index 0000000..87a84b5
--- /dev/null
+++ b/Joseph Njoroge/Chapter 15/task1.c	
@@ -0,0 +1,49 @@
+#include <stdio.h>
+#include <time.h>
+/**
+1. Rewrite the program in Listing 15.2. This time use the format specifier %c, instead
+of %s, to print out the character string of the local time on your computer
+
+include <stdio.h>
+#include <time.h>
+void GetDateTime(void);
+main()
+{
+printf(“Before the GetDateTime() function is called.\n”);
+ GetDateTime();
+ printf(“After the GetDateTime() function is called.\n”);
+ return 0;
+ }
+ /* GetDateTime() 
+ void GetDateTime(void)
+ {
+ time_t now;
+
+ printf(“Within GetDateTime().\n”);
+ time(&now);
+ printf(“Current date and time is: %s\n”,
+ asctime(localtime(&now)));
+ }
+*/
+void GetDateTime(void);
+
+
+int main(void)
+{
+    printf("Before the GetDateTime() function is called.\n");
+    GetDateTime();
+    printf("After the GetDateTime() function is called.\n");
+    return 0;
+
+}
+
+
+void GetDateTime(void)
+ {
+ time_t now;
+
+ printf("Within GetDateTime().\n");
+ time(&now);
+ printf("Current date and time is: %s\n",
+ asctime(localtime(&now)));
+ }
\ No newline at end of file
diff --git a/Joseph Njoroge/Chapter 15/task1.exe b/Joseph Njoroge/Chapter 15/task1.exe
new file mode 100644
index 0000000..9b12aca
Binary files /dev/null and b/Joseph Njoroge/Chapter 15/task1.exe differ
diff --git a/Joseph Njoroge/Chapter 15/task2.c b/Joseph Njoroge/Chapter 15/task2.c
new file mode 100644
index 0000000..5bf696b
--- /dev/null
+++ b/Joseph Njoroge/Chapter 15/task2.c	
@@ -0,0 +1,23 @@
+#include <stdio.h>
+
+/**
+2. Declare and define a function, called MultiTwo(), that can perform multiplication
+on two integer variables. Call the MultiTwo() function from the main() function
+and pass two integers to MultiTwo(). Then print out the result returned by the
+MultiTwo() function on the screen.
+*/
+int Multitwo(int, int);
+int main(void)
+{
+    int a; 
+    int b;
+
+     a = 9, b = 8;
+    printf("The multiplication of a and b is: %d\n", Multitwo(a, b));
+    return 0;
+}
+
+int Multitwo(int x, int y)
+{
+    return x * y;
+}
\ No newline at end of file
diff --git a/Joseph Njoroge/Chapter 15/task2.exe b/Joseph Njoroge/Chapter 15/task2.exe
new file mode 100644
index 0000000..36d3ecb
Binary files /dev/null and b/Joseph Njoroge/Chapter 15/task2.exe differ
diff --git a/Joseph Njoroge/Chapter 15/task3.c b/Joseph Njoroge/Chapter 15/task3.c
new file mode 100644
index 0000000..237049c
--- /dev/null
+++ b/Joseph Njoroge/Chapter 15/task3.c	
@@ -0,0 +1,86 @@
+/**
+3. Rewrite the program in Listing 15.3. This time, make a function that takes a variable
+number of int arguments and performs the operation of multiplication on
+these arguments.
+
+15L03.c: Processing variable arguments 
+#include <stdio.h>
+#include <stdarg.h>
+double MultDouble(int x, ...);
+main ()
+{
+double d1 = 1.5;
+ double d2 = 2.5;
+ double d3 = 3.5;
+ double d4 = 4.5;
+
+ printf(“Given an argument: %2.1f\n”, d1);
+ printf(“The result returned by MultDouble() is: %2.1f\n\n”,
+ MultDouble(1, d1));
+ printf(“Given arguments: %2.1f and %2.1f\n”, d1, d2);
+ printf(“The result returned by MultDouble() is: %2.1f\n\n”,
+ MultDouble(2, d1, d2));
+ printf(“Given arguments: %2.1f, %2.1f and %2.1f\n”, d1, d2, d3);
+ printf(“The result returned by MultDouble() is: %2.1f\n\n”,
+ MultDouble(3, d1, d2, d3));
+ printf(“Given arguments: %2.1f, %2.1f, %2.1f, and %2.1f\n”,
+ d1, d2, d3, d4);
+ printf(“The result returned by MultDouble() is: %2.1f\n”,
+ MultDouble(4, d1, d2, d3, d4));
+ return 0;
+ }
+ //definition of MultDouble() 
+ double MultDouble(int x, ...)
+ {
+ va_list arglist;
+ int i;
+ double result = 0.0;
+
+ printf(“The number of arguments is: %d\n”, x);
+ va_start (arglist, x);
+ for (i=0; i<x; i++)
+ result += va_arg(arglist, double);
+ va_end (arglist);
+ return result;
+ }
+*/
+
+#include <stdio.h>
+#include <stdarg.h>
+double MultDouble(int x, ...);
+ int main()
+{
+ double d1 = 6.5;
+ double d2 = 2.9;
+ double d3 = 3.5;
+ double d4 = 4.8;
+
+ printf("Given an argument: %2.1f\n", d1);
+ printf("The result returned by MultDouble() is: %2.1f\n\n",
+ MultDouble(1, d1));
+ printf("Given arguments: %2.1f and %2.1f\n", d1, d2);
+ printf("The result returned by MultDouble() is: %2.1f\n\n",
+ MultDouble(2, d1, d2));
+ printf("Given arguments: %2.1f, %2.1f and %2.1f\n", d1, d2, d3);
+ printf("The result returned by MultDouble() is: %2.1f\n\n",
+ MultDouble(3, d1, d2, d3));
+ printf("Given arguments: %2.1f, %2.1f, %2.1f, and %2.1f\n",
+ d1, d2, d3, d4);
+ printf("The result returned by MultDouble() is: %2.1f\n",
+ MultDouble(4, d1, d2, d3, d4));
+ return 0;
+ }
+ //definition of MultDouble() 
+ double MultDouble(int x, ...)
+ {
+ va_list arglist;
+ int i;
+ double result = 0.0;
+
+ printf("The number of arguments is: %f\n", x);
+ va_start (arglist, x);
+ for (i=0; i<x; i++)
+ result *= va_arg(arglist, double);
+ va_end (arglist);
+ return result;
+ }
diff --git a/Joseph Njoroge/Chapter 15/task3.exe b/Joseph Njoroge/Chapter 15/task3.exe
new file mode 100644
index 0000000..3214da9
Binary files /dev/null and b/Joseph Njoroge/Chapter 15/task3.exe differ
diff --git a/Joseph Njoroge/Chapter 15/task4.c b/Joseph Njoroge/Chapter 15/task4.c
new file mode 100644
index 0000000..7faf747
--- /dev/null
+++ b/Joseph Njoroge/Chapter 15/task4.c	
@@ -0,0 +1,44 @@
+/**
+Rewrite the program in Listing 15.3 again. This time, print out all arguments
+passed to the AddDouble() function. Does va_arg() fetch each argument in the
+same order (that is, from left to right) of the argument list passed to AddDouble()?
+*/
+#include <stdio.h>
+#include <stdarg.h>
+
+double AddDouble(int x, ...);
+
+int main()
+{
+double d1 = 1.5;
+double d2 = 2.5;
+double d3 = 3.5;
+double d4 = 4.5;
+printf("Given an argument: %2.1f\n", d1);
+printf("The result returned by AddDouble() is: %2.1f\n\n",
+AddDouble(1, d1));
+printf("Given arguments: %2.1f and %2.1f\n", d1, d2);
+printf("The result returned by AddDouble() is: %2.1f\n\n",
+AddDouble(2, d1, d2));
+printf("Given arguments: %2.1f, %2.1f and %2.1f\n", d1, d2, d3);
+printf("The result returned by AddDouble() is: %2.1f\n\n",
+AddDouble(3, d1, d2, d3));
+printf("Given arguments: %2.1f, %2.1f, %2.1f, and %2.1f\n",
+d1, d2, d3, d4);
+printf("The result returned by AddDouble() is: %2.1f\n",
+AddDouble(4, d1, d2, d3, d4));
+return 0;
+}
+/* definition of AddDouble() */
+double AddDouble(int x, ...)
+{
+va_list arglist;
+int i;
+double result = 0.0;
+printf("The number of arguments is: %d\n", x);
+va_start (arglist, x);
+for (i=0; i<x; i++)
+result += va_arg(arglist, double);
+va_end (arglist);
+return result;
+}
diff --git a/Joseph Njoroge/Chapter 15/task4.exe b/Joseph Njoroge/Chapter 15/task4.exe
new file mode 100644
index 0000000..839b02c
Binary files /dev/null and b/Joseph Njoroge/Chapter 15/task4.exe differ
diff --git a/Joseph Njoroge/Chapter 16/task1.c b/Joseph Njoroge/Chapter 16/task1.c
new file mode 100644
index 0000000..aaa0d47
--- /dev/null
+++ b/Joseph Njoroge/Chapter 16/task1.c	
@@ -0,0 +1,19 @@
+#include <stdio.h>
+
+int main()
+{
+    char str[] = "My name is Joseph";
+    int list[] = {1, 2, 3, 4, 5};
+    char *str_ptr = str;
+    int *int_ptr = list;
+
+    printf("Before the change: %s\n", str);
+    *(str_ptr + 3) = 'N';
+    printf("After the change: %s\n", str);
+
+    printf("Before the list: %d\n", list[1]);
+    *(int_ptr + 1) = 78888;
+    printf("Before the list: %d\n", list[1] );
+
+    return 0;
+}
\ No newline at end of file
diff --git a/Joseph Njoroge/Chapter 16/task1.exe b/Joseph Njoroge/Chapter 16/task1.exe
new file mode 100644
index 0000000..57be4a0
Binary files /dev/null and b/Joseph Njoroge/Chapter 16/task1.exe differ
diff --git a/Joseph Njoroge/Chapter 16/task2.c b/Joseph Njoroge/Chapter 16/task2.c
new file mode 100644
index 0000000..c661599
--- /dev/null
+++ b/Joseph Njoroge/Chapter 16/task2.c	
@@ -0,0 +1,20 @@
+#include <stdio.h>
+
+/**
+Given a character string, I like C!, write a program to pass the string to a function
+that displays the string on the screen.
+*/
+void stringingify(char *ptr);
+
+int main()
+{
+    char str[] = "I like C!";
+    char *str_ptr;
+    str_ptr = str;
+    stringingify(str_ptr);
+}
+
+void stringingify(char *ptr)
+{
+    printf("%s", ptr);
+}
\ No newline at end of file
diff --git a/Joseph Njoroge/Chapter 16/task2.exe b/Joseph Njoroge/Chapter 16/task2.exe
new file mode 100644
index 0000000..108702f
Binary files /dev/null and b/Joseph Njoroge/Chapter 16/task2.exe differ
diff --git a/Joseph Njoroge/Chapter 16/task3.c b/Joseph Njoroge/Chapter 16/task3.c
new file mode 100644
index 0000000..7410873
--- /dev/null
+++ b/Joseph Njoroge/Chapter 16/task3.c	
@@ -0,0 +1,24 @@
+#include <stdio.h>
+
+/**
+Rewrite the program in exercise 1. This time, change the string of I like C! to I
+love C! by moving a pointer that is initialized with the start address of the string
+and updating the string with new characters. Then, pass the updated string to the
+function to display the content of the string on the screen.
+*/
+
+void stringy(char *ptr);
+int main()
+{
+    char str[] = "I love C!";
+    char str2[] = "I like C!";
+    char *char_ptr;
+    char_ptr = str;
+    stringy(char_ptr);
+    return 0;
+}
+
+void stringy(char *ptr)
+{
+    printf("%s", ptr);
+}
\ No newline at end of file
diff --git a/Joseph Njoroge/Chapter 16/task3.exe b/Joseph Njoroge/Chapter 16/task3.exe
new file mode 100644
index 0000000..14a504a
Binary files /dev/null and b/Joseph Njoroge/Chapter 16/task3.exe differ
diff --git a/Joseph Njoroge/Chapter 16/task4.c b/Joseph Njoroge/Chapter 16/task4.c
new file mode 100644
index 0000000..f41fbe7
--- /dev/null
+++ b/Joseph Njoroge/Chapter 16/task4.c	
@@ -0,0 +1,13 @@
+#include <stdio.h>
+
+/**
+Given a two-dimensional character array, str, that is initialized as
+char str[2][15] = { “You know what,”, “C is powerful.” };
+write a program to pass the start address of str to a function that prints out the
+content of the character array.
+*/
+
+int main()
+{
+    
+}
\ No newline at end of file
diff --git a/Joseph Njoroge/Chapter 8/task5.c b/Joseph Njoroge/Chapter 8/task5.c
index 7c05849..f9a6933 100644
--- a/Joseph Njoroge/Chapter 8/task5.c	
+++ b/Joseph Njoroge/Chapter 8/task5.c	
@@ -8,9 +8,16 @@ characters entered by the user until the character q is accounted. (Hint: Put x!
 
 int main(void)
 {
-    char c = ' ';
-    c = getchar();
-    c != 'q' ? 1 : 0;
+    char c;
+    printf("Enter a character: ");
+
+    for (c = ' '; c != 'A' &&  c != 'a';)
+    {
+        c = getc(stdin);
+        //printf("%c", c);
+        putchar(c);
+    }
+    printf("\nOut of the loop\n");
 
     return 0;
 }
\ No newline at end of file
diff --git a/Joseph Njoroge/Chapter 8/task5.exe b/Joseph Njoroge/Chapter 8/task5.exe
index 1550a16..35dd5ef 100644
Binary files a/Joseph Njoroge/Chapter 8/task5.exe and b/Joseph Njoroge/Chapter 8/task5.exe differ
diff --git a/Joseph Njoroge/Chapter 8/tempCodeRunnerFile.c b/Joseph Njoroge/Chapter 8/tempCodeRunnerFile.c
new file mode 100644
index 0000000..3d4c6b7
--- /dev/null
+++ b/Joseph Njoroge/Chapter 8/tempCodeRunnerFile.c	
@@ -0,0 +1 @@
+ 0;
\ No newline at end of file
diff --git a/Joseph Njoroge/Chapter 9/task1.c b/Joseph Njoroge/Chapter 9/task1.c
index 759b041..cff5b2f 100644
--- a/Joseph Njoroge/Chapter 9/task1.c	
+++ b/Joseph Njoroge/Chapter 9/task1.c	
@@ -17,6 +17,6 @@ int main(void)
     x = 0xAB78;
     y = 0xAB78;
 
-    printf("The decimal value of x and y are %d and %u respectively.\n", x, y);
+    printf("The decimal value of x and y are %d and %d\n respectively.\n", x, y);
     return 0;
 }
\ No newline at end of file
diff --git a/Joseph Njoroge/Chapter 9/task1.exe b/Joseph Njoroge/Chapter 9/task1.exe
index 95e2f1b..d6d5e50 100644
Binary files a/Joseph Njoroge/Chapter 9/task1.exe and b/Joseph Njoroge/Chapter 9/task1.exe differ
diff --git a/test1.c b/test1.c
new file mode 100644
index 0000000..c31185c
--- /dev/null
+++ b/test1.c
@@ -0,0 +1,12 @@
+#include <stdio.h>
+
+
+int main()
+{
+int num;
+printf("Enter a single digit that can be divided\nby both 2 and 3:\n");
+for (num = 1; (num%2 != 0) || (num%3 != 0);)
+    num = getchar() - '0';
+ printf("You got such a number: %d\n", num);
+ return 0;
+}
\ No newline at end of file
diff --git a/test1.exe b/test1.exe
new file mode 100644
index 0000000..effeeb1
Binary files /dev/null and b/test1.exe differ