c++ - Using a 2D array in an equation -

recently i've been working on engine thrust calculates slope @ given values.

i've gotten lot of code work, cant seem equation function working. person supposed list values based off specific points on graph , newton, , give time thats different , computer find value in between time given , slope calculation.

of course thats not working , i'm lost @ point, i'm 100% sure loop wrong in function, i'm not sure equation wrong.

basically program supposed this

x   y .19 14.5 .24  6.0 .40  4.4  enter time: .21  ((.21-.19)/.24-.19))*(6-14.5)+14.5=11.1  thrust @ time .21 11.1 

source

#include <iostream> #include <cstdlib> #include <cmath> #include <string> #include <iomanip> #include <fstream> using namespace std;  const int grid_rows=50; const int grid_cols=2;  double slope(double thrust[grid_rows][grid_cols],double time);  // constant declarations const double pi = 3.1415926535; // radius/diameter of circle  // main program int main( ) {  system("cls");  cout << "take home #12 - "     << "cetua\n\n";  double thrust[grid_rows][grid_cols]; double time; double newton; char ans; int i=0; int j=0;  cout << "enter thrust curve data (0 thrust end list): "<<endl; for(i=0;i < grid_rows; i++) {     for(j=0; j< grid_cols;j++)     {         cin >> thrust[i][j];         if(thrust[i][j]==0)         {             break;         }     }     if(thrust[i][j]==0)     {         break;     }   }       {     cout << "enter time: "<<endl;     cin >> time;      newton=slope(thrust,time);      cout << "the thrust @ time "<<time << " " << newton << " newtons."                 <<endl:     cout << "would thrust value? (y or n): " <<endl;     cin >> ans;   }while(ans=='y'||ans=='y'); }  double slope(double thrust[50][2],double time) {   double newton;    while(time > thrust[50][2]);   {     for(int i=0;i < grid_rows; i++)     {       for( int j=0; j< grid_cols;j++)       {         newton=((time - thrust[i][j])/(thrust[i][j]-thrust[i][j]))             *(thrust[i][j]-thrust[i][j])+thrust[i][j];         return newton;       }     }    }  } 

double slope(double thrust[50][2],double time) {   double newton;    while(time > thrust[50][2]);   {     for(int i=0;i < grid_rows; i++)     {       for( int j=0; j< grid_cols;j++)       {         newton=((time - thrust[i][j])/(thrust[i][j]-thrust[i][j]))             *(thrust[i][j]-thrust[i][j])+thrust[i][j];         return newton;        }     }    }  } 

i see few problems algo.

1)you divide 0 error here.

((time - thrust[i][j])/(thrust[i][j]-thrust[i][j])) 

2) loop never run (always return on first iteration).

return newton;  

3) if fix (2) remember may forever trapped in while loop, (value of time , thrust[50][2] never changed).

also ";" @ end of while loop deliberate?

while(time > thrust[50][2]); 

you may want change slope method following.

double slope (double x1, double x2, double y1, double y2, double time){      double result = 0;     if ((x2-x1) != 0 ){ // google 'double comparison" may want use epsilon instead         result = ((time - x1)/(x2-x1)) * (y2-y1) + y1     }      return result; } 

to use want thing along following.

... assuming trust      [row][0] contains x     [row][1] contains y     double [lastentry-1] results; for(int i=0; i< lastentry-1; i++){      results[i] = slope ( thrust[i][0],  //x1                          thrust[i+1][0],//x2                          thrust[i][1],  //y1                          thrust[i+1][1],//y2                           time); } 

i leave how populate thrust cin exercise you.