CMIS 102 Lab 5 – Weighted Average Overview Solved


This hands-on lab allows you to follow and experiment with the critical steps of developing a program including the program description, analysis, test plan, design (using pseudocode), and implementation with C code.  The example provided uses sequential, selection and repetition statements.

Program Description
This program will calculate the weighted average of 5 numbers. The program will ask the user to enter 5 numbers treated as weights and 5 numbers to be averaged. The program will use a loop to input the data.

Analysis
I will use sequential, selection and repetition programming statements. 

I will define one integer number:  count count will store how many times valid weights and values have been entered.

I will define a variety of doubles: weight, value, sum, sumw, avg value will store the input value

weight will store the input weight for that value sum will store the running sum of values and weights sumw will store the running of the weights avg will store the weighted average of the 5 numbers and 5 weights input.

The running sum will be calculated by this formula:

sum = sum + value * weight

For example, if the first value and weight pair entered is 4, 1 and second pair is 10, 3: 

sum = sum + value*weight = 0 + 4*1 sum = 4 + 10*3 = 34 sumw = 1 + 3 = 4

Values and sum are to be input and calculated within a repetition loop:

while count < 5

  Input value, weight   sumw = sumw + weight   sum = sum + value   count = count + 1

End while

Avg is calculated by:

avg = sum / sumw

                 

A selection statement can be used inside the loop to make sure the input weight is positive.

If weight = 0 then   sumw = sumw + weight   sum = sum + value * weight   count = count + 1 Else    report error End If

Test Plan
This program is complex enough to require a variety of test cases – here are a few telling ones:

 

Test Case
Input: value weight pairs
Expected Output
Notes
1
0 1 4 1 3 0 4 0 5 0
Average = 2
Average 0 and 4

Values 3, 4, 5 just help keep input easier to follow - since weights are 0, those values are ignored.
2
1 0 2 0 3 0 0 1 5 1
Average = 2.5
Average of 0 and 5, even weights

Values 1, 2, 3 are ignored
3
0 1 20 3 3 0 4 0 5 0
Average = 15
Weighted average of 0 and 20,  with ¼ to 0 and ¾ to 20
4
2 1 2 1 3 1 5 1 5 1
Average = 3.4
Even weights, so 17/5 = 3.4
5
85 .1 88 .1 93 .2 87 .3 96 .3
Average = 90.8
Weighted average of grades, using fractions
6
85 10 88 10 93 20 87 30 96 30
Average = 90.8
Same using percentages
                 

Pseudocode
// This program will calculate the average of value-weight pairs of doubles

// Declare variables

Declare count as Integer

Declare avg, value, weight, sum, sumw as doubles

 

//Initialize values

Set count=0

Set sum = 0.0

Set sumw = 0.0

Set avg = 0.0;

// Loop through 5 value-weight pairs as doubles

While count < 5

  Print “Enter a value and its weight: ”   Input value, weight   if (weight =0)     sum = sum + value*weight     sumw = sumw + weight     count=count+1   else 

    Print (“Weight must be positive”);

  End if

End While

// Calculate average avg = sum/sumw

// Print results 

Print “Average is “ + avg 

                 

C  Code
The following is the C Code that will compile to execute in the online compilers.

// C code

// This program will calculate  //   the weighted average of 5 numbers.

// Developer: Faculty CMIS102

// Date: Jan 31, XXXX #include <stdio.h

 int main () {

/* variable definition: */    int count;    double avg, value, weight, sum, sumw;

/* Initialize */    count = 0;    sum = 0;    sumw = 0;    avg = 0.0;

// Loop through to input values    while (count < 5) {       printf("Enter a value and its weight: ");       // use %lf for double, %f for float       scanf("%lf %lf", &value, &weight);       if (weight = 0) {          sumw = sumw + weight;          sum = sum + value * weight;          count = count + 1;

      }       else {          printf("Weight must be positive\n");

      } // end if weight ok

   } // end reading input values and weights // Calculate avg if sumw is not 0    avg = sum / sumw;    printf("average is %lf\n " , avg );    return 0; } // end main

 

                 

Setting up the code and the input parameters in repl.it:

This screen shot shows the program running with the input values of 2 1 2 1 3 1 5 1 5 1, with the resulting weighted average of 3.4. In this case, since all the weights are equal, the result is the simple average of the numbers {2, 2, 3, 5, 5} = 17/5.

 

 

                 

Learning Exercises for you to complete  
1.       Demonstrate you successfully followed the steps in this lab by preparing screen captures of you running the lab as specified in the Instructions above.

 

2.       Change the code to average 10 value-weight pairs of doubles as opposed to 5. Support your experimentation with screen captures of executing the new code.

 

3.       Prepare a new test table with at least 3 distinct test cases listing input and expected output for the new code you created averaging 10 doubles.

 

4.       What happens if you entered a value other than a double? (For example a string). Support your experimentation with screen captures of executing the code.

 

5.       Modify the code to allow the user to enter any number of pairs and calculate the average. In other words, the user could enter any number of pairs as long as the weight is positive. (Hint: You can prompt the user for how many they want to enter. Or; you could use a sentinel value to trigger when the user has completed entering values). Prepare a new test table with at least 3 distinct test cases listing input and expected output for the code you created. Support your experimentation with screen captures of executing the new code.