For the following three C programs and the output samples. Explain what these programs do.

#include<stdio.h>

int main()

{

      int count = 0;

      char letter_grade ='x';

      int a = 0, b = 0, c = 0, d = 0, e = 0;

      int student_ID = 1;

      double test1 = 0.0, test2 = 0.0, final_test = 0.0, semester_average = 0.0, class_average = 0.0;

      do

      {

            printf("Enter student ID, 0 to terminate: ");

            scanf("%d", &student_ID);

           if(student_ID != 0)

            {

                printf("Enter score #1: ");

                scanf("%lf", &test1);

                printf("Enter score #2: ");

                scanf("%lf", &test2);

                printf("Enter score #3: ");

                scanf("%lf", &final_test);

                printf("%d have the following scores: %lf, %lf and %lf\n", student_ID, test1, test2, final_test);

                semester_average = (0.20*test1) + (0.30*test2) + (0.50*final_test);

                printf("The semester average score for %d is %lf\n", student_ID, semester_average);

               if(semester_average >= 80)

                    { letter_grade = 'A'; a++; }

               elseif (semester_average >= 65)

                    { letter_grade = 'B'; b++; }

               elseif (semester_average >= 50)

                    { letter_grade = 'C'; c++; }

               elseif (semester_average >= 40)

                    { letter_grade = 'D'; d++; }

               elseif(semester_average >= 0)

                   { letter_grade = 'E'; e++; }

                printf("The grade for %d is %c\n", student_ID, letter_grade);

                count++;

                printf("Student #: %d\n", count);

            }

      }while(student_ID != 0);

      printf("\nTotal number of student: %d\n", count);

      printf("\nThe number of grade A student is: %d\n", a);

      printf("The number of grade B student is: %d\n", b);

      printf("The number of grade C student is: %d\n", c);

      printf("The number of grade D student is: %d\n", d);

      printf("The number of grade E student is: %d\n", e);

      class_average = ((4*a) + (3*b) + (2*c) + (1*d))/count;

      printf("\nThe class average is: %lf\n", class_average);

      return 0;

}

Using the do-while loop, this program keeps reading student number and their marks for three subjects until 0 is entered. Then an average mark will be calculated and be assigned appropriate grade for the student using the if-else statement. When the input is terminated, a total number for every grade obtained will be displayed and finally the average grade for the whole class will be determined.

#include<stdio.h>

// Function prototype

void process(int []);

void display(int [], int);

int main()

{

     // define an int array variable with 30 integer values

      int myarray[30] = {3, -4, 1, 7, 9, -10, 12, -11, -21, 15,

                                    -5, 9, 33, -41, 31, 17, -18, 54, 2, -13,

                                    13, -27, -31, 44, 40, 51, 62, -12, -17, -37};

     // call process() function, bringing the pointer to the

     // first array element...

      process(myarray);

      return 0;

}

// the array name is the pointer to the first element

// of the array. This function process an array. Find the positive number and

// store it in positive[] array, and negative number in negative[] array

// the sort those array in ascending

void process(int bringarray[30])

{

     // define an index

      int i, j = 0, k = 0;

      int positive[30];

      int negative[30];

      printf("The original array is:\n");

      for(i=0; i<=29;i++)

      {

            printf("%d ", bringarray[i]);

           if(bringarray[i] >= 0)

            {

                  positive[j] = bringarray[i];

                 // Final value of j is the limit/max though

                 // given the array size is 30

                  j = j + 1;

            }

           // else (negative number) put it in negative[] array

           else

            {

                  negative[k] = bringarray[i];

                 // Final k value is the limit/max

                  k = k +1;

            }

      }

      printf("\n");

      printf("Positive sorted array elements:\n");

      display(positive, j);

      printf("Negative sorted array elements:\n");

      display(negative, k);

      printf("\n");

}

// function to display the array

void display(int signarray[30], int p)

{

     // i will be used for index, q is the array size,

     // pass and hold will be use as comparison

     // count and temporary storage respectively

     // in arranging the array element ascending

      int i, q = p, pass, hold;

     // do the ascending sorting...

      for(pass = 1; pass <= q-1; pass++)

     //for every 2 array elements comparison do

     //the comparison and swap...

      for(i = 0; i <= q-2; i++)

     //set the condition...

      if(signarray[i] > signarray[i + 1])

      {

           // put the a[i] in temporary variable hold...

            hold = signarray[i];

           // put the a[i + 1] in a[i]

            signarray[i] = signarray[i + 1];

           // put the hold in a[i + 1], one swapping is

           // completed and repeat for other elements...

            signarray[i + 1] = hold;

      }

     // Finally display the supposedly sorted array...

      for(i=0; i < q -1; i++)

            printf("%d ", signarray[i]);

      printf("\n");

}

--------------------------------------------------------------

This program declare myarray array of 30 integers. This array then, sent to process() function for processing. Firstly the function displays the array content horizontally using for loop. In the for loop also, the array was iterated to separate positive and negative integers. The positive integers were stored in positive[ ] array and negative integers were stored in negative[ ] array. Finally, the positive and negative arrays were sent to display() function for printing.

#include<stdio.h>

#define day 4

#define maxsize 10

void calculatesaltax(float);

int main()

{

     // array index

      int i;

     // total working hour and array to store user input

      float sumhour = 0.0, list[maxsize];

     // getting and storing user inputs

      for(i=0; i<= day; i++)

      {

            printf("Enter your day working hours (hours), day #%d: ", i);

           // scanf("%f", &list[i]);

            scanf_s("%f", &list[i], sizeof(list));

           // calculate the total working hours

            sumhour = sumhour + list[i];

      }

     // just to re-confirm the input by displaying the input values

      printf("\nConfirm your working hours per week:\n");

      for(i=0;i<=day;i++)

            printf("%.2f ", list[i]);

     // displaying the total working hours

      printf("\nYour total working hours for this week is: %.2f\n", sumhour);

     // calling calculatesaltax() function, bringing along

     // the total working hour

      calculatesaltax(sumhour);

      return 0;

}

void calculatesaltax(float sumhour)

{

     // declaring and initializing the local variables...

      float sum1 = 0.0, sum2 = 0.0, sum3 = 0.0, hourly_rate = 300.00;

     // calculating the gazetted/basic total salary, that is < 40 working hours

      if (sumhour <= 40)

      {

            sum1 = sumhour * hourly_rate;

            printf("Total salary for gazetted hours = %f", sumhour * hourly_rate);

      }

     // calculating the total overtime salary...

      if (sumhour > 40)

      {

           // simple type conversion, may lose some precision

            sum2 = (float)((sumhour-40) * 1.5 * hourly_rate);

      }

     // total up the basic salary plus overtime...

      sum3 = sum1 + sum2;

      printf("Your total salary in this week for %.2f working hours is: USD%.2f\n", sumhour, sum3);

     // checking and classifying the tax payment category...

      if(sum3 < 0)

            printf("You don't have to pay any tax!\n");

      if((0 <= sum3) & (sum3 <= 300))

            printf("Your tax is = USD%.2f\n", (2/100)*sum3);

      if(sum3 >= 300)

            printf("Your tax is = USD%.2f\n", (100 + ((2.5/100)*sum3)));

}

------------------------------------------------------------------------

This program prompts user for working hours per week. Then the total working hours per week was calculated. Based on the total working hours per week, a total income per week was calculated by calculatesaltax() function. Based on the total working hours also, a different tax need to be paid was determined based on a different tax rate also done in calculatesaltax() function.