How can I change this C++ to C

#include<stdio.h>
#include<string>
#include<iostream>

using namespace std;

const int SIZE = 6;

// parse one equation
void Equation(string line, double coefRow[], double& coefB, string& coefVal){

    int len = int(line.length());
    bool firstItem = true;
    int j=0, m=0;
    coefVal = " ";
    
    string eq = "", item="";
    for (int i = 0; i &lt; len; i++){

        // the case like +x or -x in the start of the line
        if (line[i] == '+' || line[i] == '-'){
            if (isalpha(line[i + 1])){
                coefVal += line[i + 1];
                coefRow[j++] = (line[i] == '+') ? 1. : -1.;

                i++;
                continue;
            }
        }

        // the  last coefficient and the coefficient after the sign "="
        if (line[i] == '='){
                coefRow[j++] = atof(item.c_str()); // the  last coefficient
                item = "";
                for (int l = i + 1; l &lt; len; l++)
                    item += line[l];
                coefB = atof(item.c_str());  // the coefficient after the sign "="
                break;
            }

        if (isalpha(line[i])){
                if (firstItem){ // the case like x  in the start of the line
                firstItem = false;
                coefRow[j++] =  1.;
                }
                else coefRow[j++] = atof(item.c_str()); // the coefficient after the sign "+" or "-"
                item = "";
                m = 0;
                coefVal += line[i];
                firstItem = false;
                continue;
            }
        
        // the case when the  current symbol is not letter or sign (digit and decimal)
        if (m&gt;8)cerr &lt;&lt; "The maximum length of coefficients &gt;8\n";
                item += line[i];
                m++;
                firstItem = false;
        }

    
    
}

//Recursive function for the determinant calculation
double Determinant(double A[SIZE][SIZE], int size){

    double res = 0;
    if (size == 2)return A[1][1];  // real matrix size =1
    if (size == 3)return A[1][1] * A[2][2] - A[2][1] * A[1][2]; // real matrix size=2

    // use the first column and the new matrix with  size=size-1
    int newSize = size - 1;
    double NewA[SIZE][SIZE];
    for (int i = 1; i&lt;size;&gt;      for (int j = 1; j &lt; newSize; j++){
            for (int k = 1; k &lt; newSize; k++)
                if (k &gt;= i) NewA[j][k] = A[j+ 1][k + 1];
                else NewA[j][k] = A[j + 1][k ];
        }
        int p = (i % 2) ? 1:-1;
        res += p * A[1][i] * Determinant(NewA, newSize); //  recursive call function with smaler size
    }
        return res;
}

// Cramer's rule
void Solve(double A[SIZE][SIZE], double b[SIZE], double sol[SIZE], int size){

    double temp[SIZE][SIZE], det;
    

    //call function for the determinant calculation
    det = Determinant(A, size);


    for (int j = 1; j &lt; size; j++){


        //temp = A
        // copy A to temp
        for (int k = 1; k &lt; size; k++)
            for (int l = 1; l &lt; size; l++)
                temp[k][l] = A[k][l];


        // replace column number j to new values (b)
        for (int i = 1; i &lt; size; i++)
            temp[i][j] = b[i];
        
        /* print for the program testing 
        cout &lt;&lt; "\ntemp: \n";
            for (int k = 1; k &lt; size; k++){
                for (int l = 1; l &lt; size; l++)
                    cout &lt;&lt; temp[k][l] &lt;&lt; " ";
                cout &lt;&lt; endl;
            }
            cout &lt;&lt; "det(temp)=" &lt;&lt; Determinant(temp, size) &lt;&lt; endl;
        */  

        //the solution of the system
        sol[j] = Determinant(temp, size) / det;

    }

}



int  main(){
// Tests for the program
// string line[] = { "1578x+2345y+8452z=467", "6543x+2348y+9873z=7654", "4230x+6740y+5433z=4546" }; // size = 3
// string line[] = {"78x-45y+52z=7", "43x+48y-73z=54", "30x+40y+33z=46"}; // size = 3
// string line[] = {"50a+37b+c=-44.39", "43a+39b+c=-45.31", "52a+41b+c=-44.96"}; //size = 3
// string line[] = { "a+0b+0c=-44.39", "0a+b+0c=-45.31", "0a+0b+c=-44.96" }; //size = 3
// string line[] = {"2.25x+2.5y+4z+3t=0.5", "0.25x+42y+3.1z+0t=1.33", "4.2x+11y+0z+3t=1.5", "10x+3.2y+0z+2t=1"};  //size = 4
    string row, coefVals;
    double coefRow[SIZE], coefB;
    int i, j, size;
    double det;
    double A[SIZE][SIZE],  b[SIZE], sol[SIZE];

        do{
            cout &lt;&lt; "Number of Input equations (minimum 1 ~ maximum 5): ";
            cin &gt;&gt; size;
        } while (size &lt; 1 || size &gt; 5);
        
    cout &lt;&lt; "Please, enter the " &lt;&lt; size++ &lt;&lt; " equations \n"
         &lt;&lt; "(Equations to be entered as strings, without spaces)\n";


    for (i = 1; i &lt; size; i++){
    cin &gt;&gt; row; //
    //row=line[i - 1]; // for tests(instead input lines)
    Equation(row, coefRow, coefB, coefVals);
    for (j = 1; j &lt; size; j++)
                A[i][j] = coefRow[j - 1];
        b[i] = coefB;
    }



    cout &lt;&lt; "\nA: \n";
    for (i = 1; i &lt; size; i++){
        for (j = 1; j &lt; size; j++)
            cout &lt;&lt; A[i][j] &lt;&lt; " ";
        cout &lt;&lt; endl;
        }

    cout &lt;&lt; "\nb: \n";
    for (i = 1; i &lt; size; i++)
        cout &lt;&lt; b[i] &lt;&lt; endl;



    cout &lt;&lt; "\nVariables: \n";
    for (i = 1; i &lt; size; i++)
        cout &lt;&lt; coefVals[i] &lt;&lt; endl;



    cout &lt;&lt; "\nDeterminant= ";


    det = Determinant(A, size);
    cout &lt;&lt; det;
    if (det != 0){
        Solve(A, b, sol, size);
        cout &lt;&lt; "\nSolution: \n";
        for (i = 1; i &lt; size; i++)
            cout &lt;&lt; sol[i] &lt;&lt; endl;
    }

    else
        cout &lt;&lt; "\nSystem has not solution ";


    cin.get();
    cin.get();
    
return 0;
}