I am a beginner and practicing OOPS concepts on VS Code. I am trying to solve a simple problem where the program involves taking two complex numbers and printing out the sum, difference and product.

# This is my header file

```
#pragma once
#include <string>
class Complex
{
private:
float real1, img1, real2, img2;
public:
Complex();
Complex(float r1, float i1, float r2, float i2);
std::string calc_sum();
std::string calc_diff();
float calc_prod();
};
```

# Implementation file:

```
#include "Complex.h"
#include <iostream>
#include <string>
using namespace std;
Complex::Complex() : real1{ 0.0 }, img1{ 0.0 }, real2{ 0.0 }, img2{ 0.0 } {}
Complex::Complex(float r1,float img1,float r2, float img2):
real1{r1}, img1 {img1}, real2 {r2}, img2 {img2}{}
std::string Complex::calc_sum() {
float real_sum = real1 + real2;
float img_sum = img1 + img2;
string r_sum, i_sum;
r_sum = to_string(real_sum);
i_sum = to_string(img_sum);
string sum = r_sum + " + i(" + i_sum + ")";
return sum;
}
std::string Complex::calc_diff() {
float real_diff = real1 - real2;
float img_diff = img1 - img2;
string r_diff, i_diff;
r_diff = to_string(real_diff);
i_diff = to_string(img_diff);
string diff = r_diff + " + i(" + i_diff + ")";
return diff;
}
float Complex::calc_prod() {
float real_prod = real1 * real2;
float img_prod = img1 * img2;
return (real_prod - img_prod);
}
```

# Main.cpp

```
#include <iostream>
#include "Complex.cpp"
#include <string>
using namespace std;
int main() {
float real_1,real_2, img_1, img_2, prod;
string sum, diff;
cout << "Gathering input for 1st complex number..." << endl;
cout << "Enter real part: " << endl;
cin >> real_1;
cout << "Enter imaginary part: " << endl;
cin >> img_1;
cout << "Gathering input for 2nd complex number..." << endl;
cout << "Enter real part: " << endl;
cin >> real_2;
cout << "Enter imaginary part: " << endl;
cin >> img_2;
Complex obj;
Complex obj1(real_1, img_1, real_2, img_2);
cout << "Sum Diff and Product are: " << endl;
sum = obj.calc_sum();
diff = obj.calc_diff();
prod = obj.calc_prod();
cout << "Sum: " << " " << "Diff: " << " " << "Product: " << endl;
cout << "Sum, Diff, Prod of entered numbers are: " << endl;
sum = obj1.calc_sum();
diff = obj1.calc_diff();
prod = obj1.calc_prod();
cout << "Sum: " << " " << "Diff: " << " " << "Product: " << endl;
return 0;
}
```

# These are the errors I get:

I saw a similar question, but the suggestion there was to remove the inclusion of the `.cpp`

in the `main.cpp`

file. I tried that, but I get compilation errors saying "Complex: is an undeclared identifier".

Could anyone tell me where I am going wrong?

### >Solution :

Your `main.cpp`

‘s contents are:

```
#include<iostream>
#include "Complex.cpp"
#include<string>
```

An `#include`

in C++ is equivalent to physically inserting the contents of the included file into the including file.

Your `main.cpp`

contains everything, every last bit of what’s in `complex.cpp`

.

Everything in `complex.cpp`

gets compiled and linked twice, once by itself, once when inserted into `main.cpp`

.

This is a clear fat-finger. You obviously meant to `#include "Complex.h"`

, instead of `Complex.cpp`

, in order to include only the class declaration instead of the entire kit-and-caboodle.