i have this for my requirement assignment:
Write a search function int get_index(const float astm[?][?],
const int size) to find the array index from a given size.

can someone give me some hint on how to di it pleass?

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>
#include <stdlib.h>

using namespace std;

const int COLa = 4;
const int ROWa = 9;
const int REBAR = 2;

void discard_line(ifstream &in);
void print_ASTM_table(const float astm[ROWa][COLa]);
int get_index(const float astm[ROWa][COLa],const int size);

int main()

    float astm[ROWa][COLa] = {{0}};    // declare 2D array for astm table 1.1
    int total;              
    int choice;               //  declare choice enter by the user


    char c;

    ifstream input;
    ifstream infile;


    cout<<"Enter the number of your choice : ";
    cin>>choice;                             // the first choice
    cout<<endl;                                    


    if (choice == 1)                        // if the choice is 1
    {

    input.open("F:\\astm.txt",ios::in);

    discard_line(input);            //discard the header

    // check if file not found

    if(input.fail())
    {
        cerr<<"File not found!"<<endl;
        system("PAUSE");
        exit(1);
    }



    while(!input.eof())
    {

        // store the table ASTM standards for rebars in a two dimensional array
        for(int row =0;row<ROWa;row++)
        {           
            for(int col = 0;col<COLa;col++)
            {       
                input>>astm[row][col];
            }           
            cout<<endl;

            input.get(c);
        }

        // print ASTM table for rebars in a nice format as shown in Table 1.1.
        print_ASTM_table(astm);

    }

    }
    else if (choice == 2)              // If the choice is 2
    {
        get_index(astm,ROWa);

        cout<<"Program submenu from reading rebars from a file: "<<endl;
        cout<<"(1) Print the total weight for each rebars used."<<endl;
        cout<<"(2) print memory address of weight and diameter values for a rebars of size 3."<<endl;
        cout<<"(3) Exit "<<endl;
        cout<<"Enter the number of your choice : ";
        cin>>choice;

        if(choice == 1)
        {

            infile.open("D:\\rebars.txt",ios::in);

            discard_line(infile);

            // check if file fail to  read
            if(infile.fail())
            {
                cerr<<"File not found!"<<endl;
                exit(1);
            }


             while(!infile.eof())
            {


                for(int row = 0;row<REBAR;row++)
                {
                    for(int col = 0;col<REBAR;col++)
                    {
                        infile>>astm[row][col];
                        cout<<astm[row][col]<<"  ";



                    }
                    cout<<endl;
                }



            }

        }


    }


    else{
        system("Pause");
        return 0;
    }


    system("PAUSE");
    return 0;                   // End of the program
}

void discard_line(ifstream &in) 
{
    char c;

    do
        in.get(c);
    while (c!='\n');
}

void print_ASTM_table(const float astm[ROWa][COLa])
{

        cout<<"    Size "<<"      "<<"Lenght "<<"       "<<"Weight               "<<"          "<<"diameter(in) ";
        cout<<"\n"<<endl;

        // 2D array 
        for(int row =0;row<ROWa;row++)
        {           
            for(int col = 0;col<COLa;col++)
            {

                cout<<setw(7)<<astm[row][col]<<"       ";

            }           
            cout<<endl;   

        }
}

int get_index(const float astm[ROWa][COLa],const int size) // Search function here
{


    if(astm[ROWa][COLa] == size && COLa == 1)

    return ROWa ;


}

From your code, I'm assuming the matrix will be filled completely, so ROWa is a valid limit on number of rows to search.

If the size you search for can be in any position in a row, the best you're going to be able to do is return the row's index in which it's found. If it is in a specific column of any row, that's all you'd need.

The simplest search goes something like (1D array example):

int sch( int d[], int limit, int tgt )
{
    int i;
    for( i = 0; i < limit; i++ )
        if( d[i] == tgt )
            return i;

    return -1; //tgt not found, invalid index
}

Thanks i write again my code like this and change the calling function below as
get_index(astm,size);

int get_index(const float astm[COLa][ROWa],const int size) // Search function here
{
    int index;
    int siz;
                    // if statement of the search function

                    if (astm[COLa][ROWa]==size && COLa==1)
                    {
                         index = ROWa;
                         siz  = COLa;
                    }
                    else if(index == 0)
                    {
                         siz = 2;
                    }
                    else if(index == 1)
                    {
                         siz = 3;
                    }
                    else if(index == 2)
                    {
                         siz = 4;
                    }
                    else if (index == 3)
                    {
                         siz = 5;
                    }
                    else if(index == 4)
                    {
                         siz = 7;
                    }
                    else if(index == 5)
                    {
                         siz = 8;
                    }
                    else if(index == 6)
                    {
                         siz = 9;
                    }
                    else if(index == 7)
                    {
                         siz = 12;
                    }
                    else if(index == 8)
                    {
                         siz = 14;
                    } 
                    else
                    {
                        cout<<"not index found!"<<endl;
                    }          


     return index;
}

but the program keep saying [Linker error] undefined reference to `get_index(float const (*) [4], int)'
ld returned 1 exit status
what is wrong with my code?

You seem to be making an easy thing hard ...

See this example of reading a 2D matrix from file, printing it back and then searching it to find a point ...

// myMatrixSearch.cpp //

/*

2 5
1 2 3 4 5
6 7 8 9 0

with the leading 2, indicating the number of rows
with the next 5, indicating the number of col's

you could read this into a matrix like this (using the STL vector container) ...

*/

const char* FNAME = "matrixData.txt";

#include <iostream>
#include <iomanip> // re. setw( )
#include <fstream>
#include <vector>

using namespace std;

ostream& operator << ( ostream& os, const vector< vector < int > >& v )
{
    for( size_t i = 0; i < v.size(); ++ i )
    {
        for( size_t j = 0; j < v[i].size(); ++ j )
        {
            os << ' ' << setw(8) << v[i][j];
        }
        os << endl;
    }
    return os;
}

struct Point
{
    int x, y;
    Point() :  x(-1), y(-1) {} // NOT found value
    Point( int a, int b ) :  x(a), y(b) {}
    void print() const
    {
        cout << x << ", " << y;
    }
} ;

Point find( const vector< vector < int > >& v, int val )
{
    for( size_t i = 0; i < v.size(); ++ i )
    {
        for( size_t j = 0; j < v[i].size(); ++ j )
        {
            if( val == v[i][j] ) return Point( i, j );
        }
    }
    // else ...
    return Point(); // to indicate NOT found ...
}


int main()
{
    ifstream fin( FNAME );
    if( fin )
    {
        size_t rows, cols;
        fin >> rows >> cols;
        vector< vector< int > > mat( rows);
        for( size_t i = 0; i < rows; ++ i )
        {
            mat[i].resize( cols );
            for( size_t j = 0; j < cols; ++ j )
                 fin >> mat[i][j];
        }
        fin.close();

        cout << "Showing back the matrix ... \n" << mat << endl;

        // find 9 ...

        Point p = find( mat, 9 );
        if( p.x != -1 )
        {
            cout << 9 << " was found at row_idex, col_index = ";
            p.print();
        }

    }
    else
        cout << "\nThere was aproblem opening file "
             << FNAME << endl;
}

Edited 2 Years Ago by David W: changed variable name

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