Bjarne Stroustrup's P:PP Chapter 4 Drill - c++

Question

I've just started learning C++ and I'm working by myself through Bjarne Stroustup's P:P&P.
I am on the Chapter 4 drill.
The problem I am having seems to lie within the order of the program. If I add another closing curly brace right before the vector to close the while-statement, I get the right output for max_val and min_val. However by adding that brace, the double named sum remains at zero even though I want sum to increment by the double named number.
If I compile the program as it is written now (without the addition of the extra curly braces), I get the wrong output for min_val and max_val but the proper output for sum.
Also, as you can see at the bottom of the program, the line:
cout << " values were entered." << '\n'; is not complete. I wanted to print out the number of total values entered but left it incomplete due to frustration and need of help. I am very new to programming and any constructive criticism, no matter how harsh, would be appreciated.
#include "std_lib_facilities.h"
int main()
{
double value = 0;
double max_val = 0;
double min_val = 0;
string unit =" ";
double sum = 0;
cout << "Enter some numbers, followed by a unit of distance (m, cm, ft, inch):" << '\n';
while (cin >> value >> unit){
//determines entered value as max/min/both/neither
if (min_val == 0 && value > max_val){ // first number entered is both largest and smallest
max_val = value;
min_val = value;
cout << value << " metres is both the smallest and largest so far" << '\n';
}
else if (value < min_val){// smallest number min_val = value;
cout << min_val << " metres is the smallest so far." << '\n';
}
else if (value > max_val){// largest number max_val = value;
cout << max_val << " metres is the largest so far." << '\n';
}
else { // number between smallest and largest
cout << value << " metres is neither the smallest or largest." << '\n'; }
//convert entered unit to metres
if (unit == "m"){
value = value;
}
else if (unit == "cm"){//converts cm to metres
value = value/100;
}
else if (unit == "ft"){//converts ft to metres
value = value/3.28084;
}
else if (unit == "inch"){//converts inch to metres
value = value/39.3701;
}
else{
cout << "I dont know the unit " << unit << ".";
}
vector <double> numbers; //reads input into vector
double number = 0;
while (cin >> number) numbers.push_back(number);
for (double number: numbers) sum += number;
cout << "The largest value entered was: " << max_val << "." << '\n';
cout << "The smallest value entered was: " << min_val << "." << '\n';
cout << "The sum of the numbers entered is: " << sum << "metres" <<'\n';
cout << " values were entered." << '\n';
keep_window_open("~");
return 0;
}

Answer 1

Here is a small insight regarding the input loop, finding min_value, max_value and sum:
#include "../../std_lib_facilities.h"
int main(){
// vector holding the input values
vector<double> inputValues;
// vector-input variable
double temp = 0;
// variable holding the sum of the input
double sum = 0;
// variables holding the minimum and maximum input value
double minVal = 100000; // note the initialization values
double maxVal = -100000;
vector<string>units;
string unit;
// prompt message; value input
cout << "Enter the first value: ";
while (cin >> temp >> unit) {
cout << "Enter the next value: ";
inputValues.push_back(temp);
units.push_back(unit);
}
// conversion...
for (int i = 0; i < inputValues.size(); ++i){
if (inputValues[i] > maxVal){ maxVal = inputValues[i]; }
if (inputValues[i] < minVal){ minVal = inputValues[i]; }
sum += inputValues[i];
}
// print result
cout << "Minimum temperature = " << minVal << endl;
cout << "Maximum temperature = " << maxVal << endl;
cout << "Average temperature = " << sum/inputValues.size() << endl;
return 0;
}
For the conversion you can use a second container, e.g. vector to store the units and then create a loop using the same index for both values and units, with a if, else if block for each unit conversion:
vector<string> units;
for(int i = 0 ; i < inputValues.size(); ++i){
if(units[i] == "cm") inputValue[i] = inputValue[i] / 100.;
else if(units[i] == "...") inputValue[i] =...;
// ...
}
Note:
the input loop needs improvement, e.g. termination condition, think about termination keyword with do-while loop, handling of wrong input types, cin.clear(), etc.