C++ Basic While Loop: Unknown Inputs and Value Increment - c++

So I'm trying to write a program that reads unknown inputs from a data file that has a sentinel 0 or I guess an termination point for the loop.
Number of integers per line before 0 (int count).
Number of all integers in data file (int totalcount).
Number of lines in data file (int lines).
Two examples of unknown inputs from a data file:
Example One:
1 2 3 0 4 5 6 7 0
Example Two:
0 9 11 -11
1 1 0 0 2
0
Here is my program (without "count" because that is where my problem lies):
int main()
{
//Declaring variables.
int input, lines, count, totalcount, datafile;
lines = 0;
count = 0;
totalcount = 0;
//Loop runs as long as data file has an integer to take in.
while(cin >> datafile)
{
//If datafile is not 0, loop runs until datafile is 0.
while(datafile != 0)
{
//Counts all integers in the file except 0.
totalcount += 1;
cin >> datafile;
}
//Counts how many lines there are in a data file using sentinel 0 (not "/n").
if(datafile == 0)
lines += 1;
//Outputs.
cout << lines << setw(11) << count << setw(11) << totalcount << endl;
}
return 0;
}
Please do not worry about technicality, efficiency, or anything else besides the logic/concept itself as I'm just trying to find the missing link in my knowledge to complete this assignment.
With that said, my expected outputs are as formatted:
"Line #" "Counts of integers per line" "Total counts of all integers in data file"
Using example one with my current code, I would have outputs (spacing is not exact and '.' is for blanks):
1......0......3
2......0......7
Correct expected outputs:
1......3......3
2......4......7
I would like any hints or explanation of how I can count the integers per line (before sentinel 0) and assign that value to "int count" without the value persisting to the next line.
I'm a student in an introductory C++ class so please show me a basic way of how I may go about this first and then any other advanced options as necessary for future applications.
Code of Conduct Personal Statement:
By participating, you are providing necessary knowledge for assignment completion, not completing the assignment itself. The example used is generated by me intended for concept demonstration purposes and is only a small part of the final assignment.
10/23/2016 9:56PM Update 1:
Currently attempting to use a "temp" variable to substract from "totalcount". I will update my code if attempt is successful.

totalcount is sum of counts. This is my suggestion
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
//Declaring variables.
int input, lines, count, totalcount, datafile;
lines = 0;
count = 0;
totalcount = 0;
//Loop runs as long as data file has an integer to take in.
while(cin >> datafile)
{
// Add count to totalcount and reset count each time reach 0
if (datafile == 0) {
totalcount += count;
lines += 1;
cout << lines << setw(11) << count << setw(11) << totalcount << endl;
count = 0;
}
//otherwise increase count
else {
count++;
}
}
return 0;
}

Related

Using fscanf to read from tabbed file with ints and floats in C++

I have looked for a day or so on StackOverflow and other sites, and I can't find a solution to my problem. There are some that are similar, but I can't seem to make them work.
I have a tab-delimited .txt file. One line contains a heading, and 500 lines after that each contain an integer, an integer, a float, an integer, and an integer, in that order. I have a function that is supposed to read the first and third values (the first integer and the float) from each line. It skips the first line. This is in a do-while loop, because I need to be able to process files of different lengths. However, it's getting stuck in the loop. I have it set to output the mean, but it just outputs zeros forever.
void HISTS::readMeans(int rnum) {
int r;
char skip[500];
int index = 0; int area = 0; double mean = 0; int min = 0; int max = 0;
FILE *datafile = fopen(fileName,"r");
if(datafile == NULL) cout << "No such file!\n";
else {
//ignore the first line of the file
r = fscanf(datafile,"%s\n",skip);
cout << skip << endl; //just to check
//this is the problematic code
do {
r = fscanf(datafile,"%d\t%d\t%f\t%d\t%d\n",&index,&area,&mean,&min,&max);
cout << mean << " ";
} while(feof(datafile) != 1)
}
fclose(datafile);
}
Here is a sample data file of the format I'm trying to read:
Area Mean Min Max
1 262144 202.448 160 687
2 262144 201.586 155 646
3 262144 201.803 156 771
Thanks!
Edit: I said I need to read the first and third value, and I know I'm reading all of them. Eventually I need to store the first and third value, but I cut that part for the sake of brevity. Not that this comment is brief.
You should do it C++ style,
#include <iostream>
#include <fstream>
int main() {
std::ifstream inf("file.txt");
if (!inf) { exit(1); }
int idx, area, min, max;
double mean;
while (inf >> idx >> area >> mean >> min >> max) {
if (inf.eof()) break;
std::cout << idx << " " << area << " " << mean << " " << min << " " << max << std::endl;
}
return 0;
}
It is :
1) Easy to read.
2) Less code, so less chance of error.
3) Correct handling of EOF.
Although I have left handling of first line, that is upto you.
fscanf returns the number of arguments read. Thus, if it returns less than 5 you should exit the loop.
OP ended up using operator>>, which is the correct way to do this in C++. However, for the interested C reader, there were a couple of issues in the code posted:
mean was declared as double but read using the wrong format specifier %f instead of %lf.
The first line wasn't completely read, but only the first token, Area.
A possible way to implement the desired task is as follows:
r = fscanf(datafile,"%[^\n]\n",skip);
// ^^^^^ read till newline
while ( (r = fscanf(datafile,"%d%d%lf%d%d",&index,&area,&mean,&min,&max)) == 5 ) {
// ^^ correct format specifier for double
// ...
}

C++: using for loop to allow user input of numbers into array

I'm new to the community and to coding as well. Right now I'm taking Intro to Computer Science at my CC and we're learning C++. Anyways, I have to create a program which asks the user for a number, which will be the size indicator of the array new_array. The program then asks the user to input the numbers one by one and afterwards, outputs them in reverse.
#include
using namespace std;
int main()
{
cout << "How many numbers?\n";
int numbers; // holds amount of numbers to be entered into array
cin >> numbers;
int new_array[numbers];
for(int counter = 0; counter < numbers; counter++)
{
cout << "Enter number " << counter << endl;
cin >> new_array[counter];
}
cout << "You entered: " << endl;
for(int i = numbers; i >= 0 ; i-- )
{
cout << new_array[i] << endl;
}
return 0;
}
I understand how to do this and for the most part, my program worked. It outputs the numbers entered in reverse just fine, but before it does so, it outputs large, strange numbers. For example, if the user enters 5 as the amount of numbers to be entered, and then enters 1, 2, 3, 4 and 6 as the 5 numbers respectively, the program outputs the number 4669476 first and then outputs the numbers in the array in reverse. Can anyone explain to me what I did wrong and how I could fix this? Thank you in advanced!
PS be gentle! I'm a newbie at this
This loop reads out of bounds:
for(int i = numbers; i >= 0 ; i-- )
{
If you follow i through in your head you will see that you output entries numbers through to 0, when in fact you should output entries numbers-1 through to 0.
An alternative patterns is:
for( int i = numbers; i--; )
Or you can use the fabled --> operator.
It would be possible to "simply" start from numbers - 1, however the loop pattern you have used would not work for an unsigned counter (because they are always >= 0). IMHO it is a good idea to use a pattern which works for all types; then you are less likely to make a mistake in future.
In your display for loop, you started from i = numbers which is out of the array's range. Since the array starts from 0 till size - 1, then you need to start from i = numbers - 1 all the way to >=0.
Because you start from array[numbers] which is not defined.
array[0], array[1], ... array[numbers-1] are defined.
In C arrays are stored from 0 instead of 1. So the last number is stored in array[4]
So when you're writing it out you should start an numbers - 1 instead of just numbers.
Because you are starting the index from out of range giving you garbage value.
your code should look some thing like this
for(int i = numbers-1; i >= 0 ; i-- )
{
cout << new_array[i] << endl;
}

Output from array is wrong

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <fstream>
using namespace std;
void make_array(ifstream &num, int (&array)[50]);
int main(){
ifstream file; // variable controlling the file
char filename[100]; /// to handle calling the file name;
int array[50];
cout << "Please enter the name of the file you wish to process:";
cin >> filename;
cout << "\n";
file.open(filename);
if(file.fail()){
cout << "The file failed to open.\n";
exit(1);
}
else{
cout << "File Opened Successfully.\n";
}
make_array(file, array);
file.close();
return(0);
}
void make_array(ifstream &num, int (&array)[50]){
int i = 0; // counter variable
while(!num.eof() && i < 50){
num >> array[i];
i = i + 1;
}
for(i; i>=0; i--){
cout << array[i] << "\n";
}
}
Alright, so this it my code so far. When I output the contents of the array, I get two really large negative numbers before the expected output. For example, if the file had 1 2 3 4 in it, my program is outputting -6438230 -293948 1 2 3 4.
Can somebody please tell me why I am getting these ridiculous values?
Your code outputs the array backwards, and also it increments i twice after it has finished reading all the values. This is why you see two garbage values at the start. I suspect you are misreporting your output and you actually saw -6438230 -293948 4 3 2 1.
You end up with the extra increments because your use of eof() is wrong. This is an amazingly common error for some reason. See here for further info. Write your loop like this instead:
while ( i < 50 && num >> array[i] )
++i;
Now i holds the number of valid items in the list. Assuming you do actually want to output them backwards:
while ( i-- > 0 )
cout << array[i] << "\n";
To output them forwards you'll need two variables (one to store the total number of items in the array, and one to do the iteration)
The check !num.eof() only tells you that the last thing you read was not eof. So, if your file was 1 2 3 4, the check will only kick in after the 5th num>>array[i] call. However, for that i, array[i] will be populated with a meaningless value. The only correct way to deal with eofs is to check for validity on every call to operator>>. In other words, the right condition is simply num>>array[i]. This works by exploiting this conversion to bool since C++11 and to void* pre-C++11.

I'm Having Trouble Skipping Certain Characters from an Input Text File (C++)

(I apologize that this is so low level compared to most of the questions I have seen on this website, but I have run out of ideas and I do not know who else to ask.)
I am working on a school project that requires me to read basketball statistics from a file named in06.txt. The file in06.txt looks exactly as follows:
5
P 17 24 9 31 28
R 4 5 1 10 7
A 9 2 3 6 8
S 3 4 0 5 4
I am required to read and store the first number, 5, into a variable called "games." From there, I must read the numbers from the second line and determine the high, the low, and the average. I must do the same thing for lines 3, 4, and 5. (FYI, the letters P, R, A, and S are there to indicate "Points," "Rebounds," "Assists," and "Steals.")
Since I only have been learning about programming for a few weeks, I do not want to overwhelm myself by jumping right into dealing with every aspect of the project. So, I am first working on determining the average from each line. My plan is to keep a running total of each line and then divide the running total by the number of games, which is 5 in this case.
This is my code:
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
int main()
{
int games;
int points_high, points_low, points_total;
int rebounds_high, rebounds_low, rebounds_total;
int assists_high, assists_low, assists_total;
int steals_high, steals_low, steals_total;
double points_average, rebounds_average, assists_average, steals_average;
ifstream fin;
ofstream fout;
fin.open("in06.txt");
if( fin.fail() ) {
cout << "\nInput file opening failed.\n";
exit(1);
}
else
cout << "\nInput file was read successfully.\n";
int tempint1, tempint2, tempint3, tempint4;
char tempchar;
fin >> games;
fin.get(tempchar); // Takes the endl; from the text file.
fin.get(tempchar); // Takes the character P from the text file.
while( fin >> tempint1 ) {
points_total += tempint1;
}
fin.get(tempchar); // Takes the endl; from the text file.
fin.get(tempchar); // Takes the character R from the text file.
while( fin >> tempint2 ) {
rebounds_total += tempint2;
}
fin.get(tempchar); // Takes the endl; from the text file.
fin.get(tempchar); // Takes the character A from the text file.
while( fin >> tempint3 ) {
assists_total += tempint3;
}
fin.get(tempchar); // Takes the endl; from the text file.
fin.get(tempchar); // Takes the character S from the text file.
while( fin >> tempint4 ) {
steals_total += tempint4;
}
cout << "The total number of games is " << games << endl;
cout << "The value of total points is " << points_total << endl;
cout << "The value of total rebounds is " << rebounds_total << endl;
cout << "The value of total assists is " << assists_total << endl;
cout << "The value of total steals is " << steals_total << endl;
return 0;
}
And this is the (incorrect) output:
Input file was read successfully.
The total number of games is 5
The value of total points is 111
The value of total rebounds is 134522076
The value of total assists is 134515888
The value of total steals is 673677934
I have been reading about file input in my textbook for hours, hoping that I will find something that will indicate why my program is outputting the incorrect values. However, I have found nothing. I have also researched similar problems on this forum as well as other forums, but the solutions use methods that I have not yet learned about and thus, my teacher would not allow them in my project code. Some of the methods I saw were arrays and the getline function. We have not yet learned about either.
Note: My teacher does not want us to store every integer from the input file. He wants us to open the file a single time and store the number of games, and then use loops and if statements for determining the high, average, and low numbers from each line.
If anyone could help me out, I would GREATLY appreciate it!
Thanks!
You have all these variables declared:
int games;
int points_high, points_low, points_total;
int rebounds_high, rebounds_low, rebounds_total;
int assists_high, assists_low, assists_total;
int steals_high, steals_low, steals_total;
double points_average, rebounds_average, assists_average, steals_average;
And then you increment them:
points_total += tempint1;
Those variables were never initialzed to a known value (0), so they have garbage in them. You need to initialize them.
Besides what OldProgrammer said, you've approached the reading of integers incorrectly. A loop like this
while( fin >> tempint2 ) {
rebounds_total += tempint2;
}
will stop when an error occurs. That is, either it reaches EOF or the extraction encounters data that cannot be formatted as an integer - or in other words, good() returns false. It does not, as you seem to think, stop reading at the end of a line. Once an error flag is set, all further extractions will fail until you clear the flags. In your case, a loop starts reading after P, extracts five intergers, but then it encounters the R from the next line and errors out.
Change this to a loop that reads a fixed number of integers or alternatively, read a whole line using std::getline into a std::string, put it into a std::stringstream and read from there.
In any case, learn to write robust code. Check for success of extractions and count how many elements you get.
An example of a loop that reads at most 5 integers:
int i;
int counter = 0;
while (counter < 5 && file >> i) {
++counter;
// do something with i
}
if (counter < 5) {
// hm, got less than 5 ints...
}

Assign last number of a text file to a variable C++

I am doing a program that outputs a list of prime numbers with fstream.
I have this so far:
int export_list (int lim = 50)
{
int x;
last_in_txt = ????????????; // assigns last number on txt
ofstream file ("Primes.txt" , ios::app);
if (file.is_open()) // if it opens correctly
{
for (x = last_in_txt ; x < lim ; x++)
{
if (check_prime (x)) // returns 1 when x is prime, returns 0 when not
{
file<< x << " ";
}
}
cout << "Done!" << endl << pressenter;
cin.get();
}
else
{
cout << "Unable to open file" << endl << pressenter;
cin.get();
}
return(0);
}
So, as you can see, this should append a list of prime numbers to Primes.txt, starting with the prime 1234547.
Primes.txt looks like this:
2 3 5 7 11 13 17 19 23 29 31 37 (...) 1234543 1234547
My question is how do I assign 1234547 (which is the last number of the txt) to the variable last_in_txt?
Other (not so important) question:
Should I save the numbers the way I'm currently doing, or should I store each number in a separate line?
One simple way: keep reading and assign until the whole file is read.
For example,
int last_in_txt = 0;
{
ifstream infile("Prime.txt");
int k;
while(infile >> k) {
last_in_txt = k;
}
}
// Now last_in_txt is assigned properly, and Prime.txt is closed
This works well no matter the numbers in Prime.txt are separated by space characters (' ') or by newline characters ('\n').
My suggestion is that you write using binary format into the text file(using wb in C). In this case you will know how many bytes does the last number occupy and you will be able to use seekg and tellg to get it. If you use plain text format you will have to read char by char from the end and this is more error-prone and also slower.