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help with loops. (or maybe understanding problem.)

byronflds (119)
my teacher gave us an assignment to alter a previous program with loops. i cant seem to get what i am supposed to do. can someone help me to understand?

here are his instructions: 
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Convert your solution to previous assignment into
                 a program with loops.



REQUIREMENTS for Statistics (mandatory):

   0. Data values are of type float.

   1. Program must require user to enter the number of values,
      and must prompt user for each value.

      Input prompt 1: "Enter number of values: "
      Input prompt 2: "Enter next value: "

   2. Your program must avoid dividing by zero.

   3. Your program should work with these test cases:

      3  10.0 10.10 10.2 
      0
      -1 
      7  1 2 3 4 50 60 70

and here was my solution to the first program: 
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//-| ---------------------------------------------------------------
//-| Assignment ID: PROG5
//-| File name:     curve.cpp  
//-| Due:           Monday, Feb 27 at 12 pm
//-| Author: bfields Byron Fields
//-| Description:   Extend the program statistics.cpp to curve the grades on
//-|                ten exam scores. 
//-| ---------------------------------------------------------------

#include <iostream>
#include <iomanip>
using namespace std;            

int main ()
{


//-| --------------------------------------------------
//-| Declare Variables
//-| --------------------------------------------------
float SumX;
float SumXsq;
int TestScore1;
int TestScore2;
int TestScore3;
int TestScore4;
int TestScore5;
int TestScore6;
int TestScore7;
int TestScore8;
int TestScore9;
int TestScore10;
float Xavg;
float Xvar;
float Xstd;
float C_lowerbound = Xavg - 1/2 * Xstd;
float D_lowerbound = Xavg - 3/2 * Xstd;
float B_lowerbound = Xavg + 1/2 * Xstd;
float A_lowerbound = Xavg + 3/2 * Xstd;
//-| --------------------------------------------------
//-| 1. Initialize accumulators, SumX and SumXsq, to 0.
//-| --------------------------------------------------
SumX = 0;
SumXsq = 0;
//-| --------------------------------------------------
//-| 2. Repeat 10 times
//-|     2.a) Read a Score
//-|     2.b) Add Score to SumX.
//-|     2.c) Add Score*Score to SumXsq.
//-| --------------------------------------------------
cin >> TestScore1;
SumX = SumX + TestScore1;
SumXsq = SumXsq + TestScore1*TestScore1;
cin >> TestScore2;
SumX = SumX + TestScore2;
SumXsq = SumXsq + TestScore2*TestScore2;
cin >> TestScore3;
SumX = SumX + TestScore3;
SumXsq = SumXsq + TestScore3*TestScore3;
cin >> TestScore4;
SumX = SumX + TestScore4;
SumXsq = SumXsq + TestScore4*TestScore4;
cin >> TestScore5;
SumX = SumX + TestScore5;
SumXsq = SumXsq + TestScore5*TestScore5;
cin >> TestScore6;
SumX = SumX + TestScore6;
SumXsq = SumXsq + TestScore6*TestScore6;
cin >> TestScore7;
SumX = SumX + TestScore7;
SumXsq = SumXsq + TestScore7*TestScore7;
cin >> TestScore8;
SumX = SumX + TestScore8;
SumXsq = SumXsq + TestScore8*TestScore8;
cin >> TestScore9;
SumX = SumX + TestScore9;
SumXsq = SumXsq + TestScore9*TestScore9;
cin >> TestScore10;
SumX = SumX + TestScore10;
SumXsq = SumXsq + TestScore10*TestScore10;
//-| -------------------------------------------------------
//-| 3. Compute the mean (average) (Avg) using equation (d).
//-|     (d) Avg = SumX / N
//-| -------------------------------------------------------
Xavg = SumX / 10;
//-| -------------------------------------------------------      
//-| 4. Compute variance (Var) using equation (f).
//-| (f) Var = ( SumXsq - 2*Avg*SumX + N*Avg )/N
//-| -------------------------------------------------------
Xvar = ( SumXsq - 2*Xavg*SumX + 10*Xavg )/10;
//-| ----------------------------------------------------------
//-| 5. Compute standard deviation (StdDev) using equation (g).
//-| (g) StdDev = sqrt(Var)
//-| ----------------------------------------------------------
Xstd = sqrt(Xvar);
//-| ----------------------------------------------------------
//-|  6. Display the computed values.
//-|  Outputs:      
//-|               STATISTICAL ANALYSIS
//-|               ====================
//-|               SUM OF VALUES  =    xxxx.x
//-|               SUM OF SQUARES = xxxxxxx.x
//-|               AVERAGE        =    xxx.xx
//-|               VARIANCE       =  xxxxx.xx
//-|               STD DEVIATION  =    xxx.xx
//-|
//-|               ====================
//-| ----------------------------------------------------------
cout << setw(26) << "STATISTICAL ANALYSIS" << endl;
cout << setw(26) << "====================" << endl;
cout << setw(26) << "SUM OF VALUES  =    ";
cout << fixed << setprecision(2) << right << SumX << endl;
cout << setw(23) << "SUM OF SQUARES = ";
cout << fixed << setprecision(2) << SumXsq << endl;
cout << setw(26) << "AVERAGE        =    ";
cout << fixed << setprecision(2) << right << Xavg << endl;
cout << setw(24) << "VARIANCE       =  ";
cout << fixed << setprecision(2) << right << Xvar << endl;
cout << setw(26) << "STD DEVIATION  =    ";
cout << fixed << setprecision(2) << right << Xstd << endl;
cout << " " << endl;
cout << setw(26) << "====================" << endl;
//-| -----------------------------------------------------------
//-| 8. Compute the lower bound for each letter grade.
//-|          (a) C_lowerbound = Avg - 1/2 * StdDev
//-|          (b) D_lowerbound = Avg - 3/2 * StdDev
//-|          (c) B_lowerbound = Avg + 1/2 * StdDev
//-|          (d) A_lowerbound = Avg + 3/2 * StdDev
//-| -----------------------------------------------------------
C_lowerbound = Xavg - 1/2 * Xstd;
D_lowerbound = Xavg - 3/2 * Xstd;
B_lowerbound = Xavg + 1/2 * Xstd;
A_lowerbound = Xavg + 3/2 * Xstd;
//-| -----------------------------------------------------------
//-| 9. Display the score ranges for each letter grade.
//-|              GUIDE FOR CURVING GRADES
//-|                ========================
//-|
//-|              MEAN (AVG)   = xxx.xx
//-|              STD DEV (SD) = xxx.xx
//-|
//-|              Scores for A: aaa.a AND ABOVE
//-|              Scores for B: [ bbb.b - aaa.a ]
//-|              Scores for C: [ ccc.c - bbb.b ]
//-|              Scores for D: [ ddd.d - ccc.c ]
//-|              Scores for F: BELOW ddd.d
//-| -----------------------------------------------------------
cout << setw(22) << "MEAN (AVG)   =  ";
cout << fixed << setprecision(2) << right << Xavg << endl;
cout << setw(23) << "STD DEV (SD) =   ";
cout << fixed << setprecision(2) << Xstd << endl;
cout << endl;
cout << setw(20) << "Scores for A: ";
cout << fixed << setprecision(2) << right << A_lowerbound <<" AND ABOVE" << endl;
cout << setw(21) << "Scores for B: [";
cout << fixed << setprecision(2) << right << B_lowerbound << " -  " << A_lowerbound << "  ]" << endl;
cout << setw(21) << "Scores for C: [";
cout << fixed << setprecision(2) << right << C_lowerbound << " -  " << B_lowerbound << "  ]" << endl;
cout << setw(21) << "Scores for D: [";
cout << fixed << setprecision(2) << right << D_lowerbound << " -  " << C_lowerbound << "  ]" << endl;
cout << setw(26) << "Scores for F: BELOW ";
cout << fixed << setprecision(2) << right << D_lowerbound << endl;
//-| -----------------------------------------------------------
//-| Print Out Copyright
//-| -----------------------------------------------------------
cout << "(c) 2012, bfields Byron Fields" << endl;

   return 0;
}
astex (15)
It seems your teacher wants you to shorten this and make the number of test scores variable using a for loop and check for valid input using a while loop.

For example, if I wanted to get some number, n, of strings, I might have:
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unsigned int n = 0;
while (n<1) {
  std::cin>>nX;
  n = (unsigned int)std::atof(nX);
}
std::string stuff[n]
for (unsigned int i = 0; i<n; i++) {
  std::cin>>stuff[i];
}
byronflds (119)
thanks man. you just made something click in my brain.
byronflds (119)
can anyone tell me why i keep getting these errors?:
test.cpp: In function `int main()':
test.cpp:46: parse error before `)' token
test.cpp:52: parse error before `;' token
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//-| ---------------------------------------------------------------
//-| Assignment ID: PROG5
//-| File name:     curve.cpp  
//-| Due:           Monday, Feb 27 at 12 pm
//-| Author: bfields Byron Fields
//-| Description:   Extend the program statistics.cpp to curve the grades on
//-|                ten exam scores. 
//-| ---------------------------------------------------------------

#include <iostream>
#include <iomanip>
using namespace std;            

int main ()
{


//-| --------------------------------------------------
//-| Declare Variables
//-| --------------------------------------------------
float SumX;
float SumXsq;
float TestScore;
float Xavg;
float Xvar;
float Xstd;
float C_lowerbound = Xavg - 1/2 * Xstd;
float D_lowerbound = Xavg - 3/2 * Xstd;
float B_lowerbound = Xavg + 1/2 * Xstd;
float A_lowerbound = Xavg + 3/2 * Xstd;
float Rep;
float X;
//-| --------------------------------------------------
//-| 1. Initialize accumulators, SumX and SumXsq, to 0.
//-| --------------------------------------------------
SumX = 0;
SumXsq = 0;
//-| --------------------------------------------------
//-| 2. Repeat 10 times
//-|     2.a) Read a Score
//-|     2.b) Add Score to SumX.
//-|     2.c) Add Score*Score to SumXsq.
//-| --------------------------------------------------
cout << "Enter number of values: " << endl;
  cin >> X;
for(Rep == X)
{
 
while (Rep > 0) 
{ cout << "Enter next value: " << endl;
cin >> TestScore;
 SumX = SumX + TestScore;
 SumXsq = SumXsq + TestScore*TestScore;
}
}
//-| -------------------------------------------------------
//-| 3. Compute the mean (average) (Avg) using equation (d).
//-|     (d) Avg = SumX / N
//-| -------------------------------------------------------
Xavg = SumX / 10;
//-| -------------------------------------------------------      
//-| 4. Compute variance (Var) using equation (f).
//-| (f) Var = ( SumXsq - 2*Avg*SumX + N*Avg )/N
//-| -------------------------------------------------------
Xvar = ( SumXsq - 2*Xavg*SumX + 10*Xavg )/10;
//-| ----------------------------------------------------------
//-| 5. Compute standard deviation (StdDev) using equation (g).
//-| (g) StdDev = sqrt(Var)
//-| ----------------------------------------------------------
Xstd = sqrt(Xvar);
//-| ----------------------------------------------------------
//-|  6. Display the computed values.
//-|  Outputs:      
//-|               STATISTICAL ANALYSIS
//-|               ====================
//-|               SUM OF VALUES  =    xxxx.x
//-|               SUM OF SQUARES = xxxxxxx.x
//-|               AVERAGE        =    xxx.xx
//-|               VARIANCE       =  xxxxx.xx
//-|               STD DEVIATION  =    xxx.xx
//-|
//-|               ====================
//-| ----------------------------------------------------------
cout << setw(26) << "STATISTICAL ANALYSIS" << endl;
cout << setw(26) << "====================" << endl;
cout << setw(26) << "SUM OF VALUES  =    ";
cout << fixed << setprecision(2) << right << SumX << endl;
cout << setw(23) << "SUM OF SQUARES = ";
cout << fixed << setprecision(2) << SumXsq << endl;
cout << setw(26) << "AVERAGE        =    ";
cout << fixed << setprecision(2) << right << Xavg << endl;
cout << setw(24) << "VARIANCE       =  ";
cout << fixed << setprecision(2) << right << Xvar << endl;
cout << setw(26) << "STD DEVIATION  =    ";
cout << fixed << setprecision(2) << right << Xstd << endl;
cout << " " << endl;
cout << setw(26) << "====================" << endl;
//-| -----------------------------------------------------------
//-| 8. Compute the lower bound for each letter grade.
//-|          (a) C_lowerbound = Avg - 1/2 * StdDev
//-|          (b) D_lowerbound = Avg - 3/2 * StdDev
//-|          (c) B_lowerbound = Avg + 1/2 * StdDev
//-|          (d) A_lowerbound = Avg + 3/2 * StdDev
//-| -----------------------------------------------------------
C_lowerbound = Xavg - 1/2 * Xstd;
D_lowerbound = Xavg - 3/2 * Xstd;
B_lowerbound = Xavg + 1/2 * Xstd;
A_lowerbound = Xavg + 3/2 * Xstd;
//-| -----------------------------------------------------------
//-| 9. Display the score ranges for each letter grade.
//-|              GUIDE FOR CURVING GRADES
//-|                ========================
//-|
//-|              MEAN (AVG)   = xxx.xx
//-|              STD DEV (SD) = xxx.xx
//-|
//-|              Scores for A: aaa.a AND ABOVE
//-|              Scores for B: [ bbb.b - aaa.a ]
//-|              Scores for C: [ ccc.c - bbb.b ]
//-|              Scores for D: [ ddd.d - ccc.c ]
//-|              Scores for F: BELOW ddd.d
//-| -----------------------------------------------------------
cout << setw(22) << "MEAN (AVG)   =  ";
cout << fixed << setprecision(2) << right << Xavg << endl;
cout << setw(23) << "STD DEV (SD) =   ";
cout << fixed << setprecision(2) << Xstd << endl;
cout << endl;
cout << setw(20) << "Scores for A: ";
cout << fixed << setprecision(2) << right << A_lowerbound <<" AND ABOVE" << endl;
cout << setw(21) << "Scores for B: [";
cout << fixed << setprecision(2) << right << B_lowerbound << " -  " << A_lowerbound << "  ]" << endl;
cout << setw(21) << "Scores for C: [";
cout << fixed << setprecision(2) << right << C_lowerbound << " -  " << B_lowerbound << "  ]" << endl;
cout << setw(21) << "Scores for D: [";
cout << fixed << setprecision(2) << right << D_lowerbound << " -  " << C_lowerbound << "  ]" << endl;
cout << setw(26) << "Scores for F: BELOW ";
cout << fixed << setprecision(2) << right << D_lowerbound << endl;
//-| -----------------------------------------------------------
//-| Print Out Copyright
//-| -----------------------------------------------------------
cout << "(c) 2012, bfields Byron Fields" << endl;

   return 0;
}
byronflds (119)
got it to compile but not getting the desired results: 
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//-| ---------------------------------------------------------------
//-| Assignment ID: PROG5
//-| File name:     curve.cpp  
//-| Due:           Monday, Feb 27 at 12 pm
//-| Author: bfields Byron Fields
//-| Description:   Extend the program statistics.cpp to curve the grades on
//-|                ten exam scores. 
//-| ---------------------------------------------------------------

#include <iostream>
#include <iomanip>
using namespace std;            

int main ()
{


//-| --------------------------------------------------
//-| Declare Variables
//-| --------------------------------------------------
float SumX;
float SumXsq;
float TestScore;
float Xavg;
float Xvar;
float Xstd;
float C_lowerbound = Xavg - 1/2 * Xstd;
float D_lowerbound = Xavg - 3/2 * Xstd;
float B_lowerbound = Xavg + 1/2 * Xstd;
float A_lowerbound = Xavg + 3/2 * Xstd;
float Rep;
float X;
//-| --------------------------------------------------
//-| 1. Initialize accumulators, SumX and SumXsq, to 0.
//-| --------------------------------------------------
SumX = 0;
SumXsq = 0;
//-| --------------------------------------------------
//-| 2. Repeat 10 times
//-|     2.a) Read a Score
//-|     2.b) Add Score to SumX.
//-|     2.c) Add Score*Score to SumXsq.
//-| --------------------------------------------------
cout << "Enter number of values: " << endl;
  cin >> X;
while(Rep == X)
do
{

 cout << "Enter next value: " << endl;
 cin >> TestScore;
 SumX = SumX + TestScore;
 SumXsq = SumXsq + TestScore*TestScore;
}
while(Rep == X);
//-| -------------------------------------------------------
//-| 3. Compute the mean (average) (Avg) using equation (d).
//-|     (d) Avg = SumX / N
//-| -------------------------------------------------------
Xavg = SumX / 10;
//-| -------------------------------------------------------      
//-| 4. Compute variance (Var) using equation (f).
//-| (f) Var = ( SumXsq - 2*Avg*SumX + N*Avg )/N
//-| -------------------------------------------------------
Xvar = ( SumXsq - 2*Xavg*SumX + 10*Xavg )/10;
//-| ----------------------------------------------------------
//-| 5. Compute standard deviation (StdDev) using equation (g).
//-| (g) StdDev = sqrt(Var)
//-| ----------------------------------------------------------
Xstd = sqrt(Xvar);
//-| ----------------------------------------------------------
//-|  6. Display the computed values.
//-|  Outputs:      
//-|               STATISTICAL ANALYSIS
//-|               ====================
//-|               SUM OF VALUES  =    xxxx.x
//-|               SUM OF SQUARES = xxxxxxx.x
//-|               AVERAGE        =    xxx.xx
//-|               VARIANCE       =  xxxxx.xx
//-|               STD DEVIATION  =    xxx.xx
//-|
//-|               ====================
//-| ----------------------------------------------------------
cout << setw(26) << "STATISTICAL ANALYSIS" << endl;
cout << setw(26) << "====================" << endl;
cout << setw(26) << "SUM OF VALUES  =    ";
cout << fixed << setprecision(2) << right << SumX << endl;
cout << setw(23) << "SUM OF SQUARES = ";
cout << fixed << setprecision(2) << SumXsq << endl;
cout << setw(26) << "AVERAGE        =    ";
cout << fixed << setprecision(2) << right << Xavg << endl;
cout << setw(24) << "VARIANCE       =  ";
cout << fixed << setprecision(2) << right << Xvar << endl;
cout << setw(26) << "STD DEVIATION  =    ";
cout << fixed << setprecision(2) << right << Xstd << endl;
cout << " " << endl;
cout << setw(26) << "====================" << endl;
//-| -----------------------------------------------------------
//-| 8. Compute the lower bound for each letter grade.
//-|          (a) C_lowerbound = Avg - 1/2 * StdDev
//-|          (b) D_lowerbound = Avg - 3/2 * StdDev
//-|          (c) B_lowerbound = Avg + 1/2 * StdDev
//-|          (d) A_lowerbound = Avg + 3/2 * StdDev
//-| -----------------------------------------------------------
C_lowerbound = Xavg - 1/2 * Xstd;
D_lowerbound = Xavg - 3/2 * Xstd;
B_lowerbound = Xavg + 1/2 * Xstd;
A_lowerbound = Xavg + 3/2 * Xstd;
//-| -----------------------------------------------------------
//-| 9. Display the score ranges for each letter grade.
//-|              GUIDE FOR CURVING GRADES
//-|                ========================
//-|
//-|              MEAN (AVG)   = xxx.xx
//-|              STD DEV (SD) = xxx.xx
//-|
//-|              Scores for A: aaa.a AND ABOVE
//-|              Scores for B: [ bbb.b - aaa.a ]
//-|              Scores for C: [ ccc.c - bbb.b ]
//-|              Scores for D: [ ddd.d - ccc.c ]
//-|              Scores for F: BELOW ddd.d
//-| -----------------------------------------------------------
cout << setw(22) << "MEAN (AVG)   =  ";
cout << fixed << setprecision(2) << right << Xavg << endl;
cout << setw(23) << "STD DEV (SD) =   ";
cout << fixed << setprecision(2) << Xstd << endl;
cout << endl;
cout << setw(20) << "Scores for A: ";
cout << fixed << setprecision(2) << right << A_lowerbound <<" AND ABOVE" << endl;
cout << setw(21) << "Scores for B: [";
cout << fixed << setprecision(2) << right << B_lowerbound << " -  " << A_lowerbound << "  ]" << endl;
cout << setw(21) << "Scores for C: [";
cout << fixed << setprecision(2) << right << C_lowerbound << " -  " << B_lowerbound << "  ]" << endl;
cout << setw(21) << "Scores for D: [";
cout << fixed << setprecision(2) << right << D_lowerbound << " -  " << C_lowerbound << "  ]" << endl;
cout << setw(26) << "Scores for F: BELOW ";
cout << fixed << setprecision(2) << right << D_lowerbound << endl;
//-| -----------------------------------------------------------
//-| Print Out Copyright
//-| -----------------------------------------------------------
cout << "(c) 2012, bfields Byron Fields" << endl;

   return 0;
}
vin (300)
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while(Rep == X) // What is the value of Rep here??
do
{

 cout << "Enter next value: " << endl;
 cin >> TestScore;
 SumX = SumX + TestScore;
 SumXsq = SumXsq + TestScore*TestScore;
}
while(Rep == X);



Also your code for Xavg and Xvar assume always 10 values input by user.
What if user only enters 3 values?

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Xavg = SumX / 10;

//...

Xvar = ( SumXsq - 2*Xavg*SumX + 10*Xavg )/10;


Don't use integer division, use 1.0/2.0 or 0.5
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C_lowerbound = Xavg - 1/2 * Xstd; // = Xavg - 0 * Xstd = Xavg
D_lowerbound = Xavg - 3/2 * Xstd;
B_lowerbound = Xavg + 1/2 * Xstd;
A_lowerbound = Xavg + 3/2 * Xstd;


Is this formula correct? Var should not be negative.

(f) Var = ( SumXsq - 2*Avg*SumX + N*Avg )/N
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