Read line of numbers from stdin [duplicate] - c++

Question

This question already has answers here:
How to determine if a string is a number with C++?
(36 answers)
Closed 8 years ago.
I am working on program that would calculate with matrixes but i am not sure what is best way how to read matrix line by line from command line.
My goal is this:
Please enter number of lines:
2
Please enter line 1/2:
1 4 5 2
Please enter line 2/2:
1 5 7 8
At the end of this i would like to have array or vector of numbers 1,4,5,2,1,5,7,8.
This is my code:
vector<string>matrix;
string input;
int nrows;
cout << "Enter number of rows:" << endl;
cin >> nrows;
getline(cin, input);
for (int i = 1; i <= nrows; i++) {
cout << "Enter line " << i << "/" << nrows << endl;
getline(cin, input);
matrix.push_back(input);
}
for (int i = 0; i < matrix.size();i++){
cout << matrix.at(i)<<endl;
}
This reads whole line and save it into vector of string and there is much to do to separate just numbers. Is there any way how could I load only numbers in the line ? So for example for the line:
1 a 3 2 4sdsd
I would get numbers 1,3,2,4 ?
Thank for any help.

Answer 1

string process(const string& input) // Removes all characters except <space> and digits [0-9]
{
string ret;
for(int i=0; i<(int)input.size(); i++)
{
if(input[i]==' '||(input[i]>='0'&&input[i]<='9'))
ret+=input[i];
}
return ret;
}
int main()
{
int nrows;
string input;
cout<<"Enter number of rows - ";
cin>>nrows;
cin.get(); // Take the remaining <Enter>
vector<vector<int> > matrix(nrows); // A 2-D vector representing the matrix
for(int i=0; i<(int)matrix.size(); i++)
{
cout<<"Please enter line "<<i+1<<"/"<<nrows<<" -: \n";
getline(cin,input);
stringstream ss(process(input));
int num;
while(ss>>num)
{
matrix[i].push_back(num);
}
}
for(int i=0; i<(int)matrix.size(); i++) // Display the matrix
{
for(int j=0; j<(int)matrix[i].size(); j++)
{
cout<<matrix[i][j]<<" ";
}
cout<<"\n";
}
}

Answer 2

I would use a 2D vector. Also, ask the user for number of columns:
vector<vector<int>> matrix;
int nrows, ncols;
cout << "Enter number of rows:" << endl;
cin >> nrows;
cout << "Enter number of columns:" << endl;
cin >> ncols;
matrix.resize(nrows);
for (int i = 0; i < nrows; i++) {
cout << "Enter line " << (i+1) << "/" << nrows << endl;
int tmp;
while (matrix[i].size() < ncols) {
while (!(cin >> tmp)) { // Not a number. Clear cin
cin.clear();
cin.ignore(1);
}
matrix[i].push_back(tmp);
}
}

Answer 3

One way to do it:
// only allow digits and spaces
string removeNonNumbers(const string& s) {
stringstream ss;
for(int i=0; i<s.length(); ++i) {
if(isdigit(s[i]) || ' ' == s[i])
ss << s[i];
}
return ss.str();
}
vector<int> splitToInts(const string& s) {
vector<int> ret;
stringstream ssin(s);
while (ssin.good()){
string tmp;
ssin >> tmp;
ret.push_back(atoi(tmp.c_str()));
}
return ret;
}
To use it, do this when reading input in your getline loop:
vector<int> numbers = splitToInts( removeNonNumbers(input) );