C / C++ / MFC

void input_Area(void)  // ** Pt1 here you declare you are going to return nothing AKA a void
{
   float width = 0, length = 0, answer = 0;
   cout << "Enter the width of rectangle :";
   cin >> width;
   cout << "Enter the length of rectangle :";
   cin >> length;
   answer = rectangleArea(width, length);
   cout << "The area of Rectangle is : " << answer << endl;
}

#ifndef _CALCULATION_H
#define _CALCULATION_H

void input_Func(void); //Input function of text.
void input_Area(void); //Input function of Area. **** FIXED NOW MATCHES THE .CPP file
void input_Trap(void); //Input function of Trapezoid.  *** STILL BUGGED .CPP says it returns a float this says void
float rectangle_Area (float , float); //Declaration for Rectangle Area.
float trapezoid_Area (float , float, float); //Declaration for Trapezoid Area.

#endif

float input_Area(void)  // ** Pt1 here you declare you are going to return a float
{
   float width = 0, length = 0, answer = 0;
   cout << "Enter the width of rectangle :";
   cin >> width;
   cout << "Enter the length of rectangle :";
   cin >> length;
   answer = rectangleArea(width, length);
   cout << "The area of Rectangle is : " << answer << endl;

   return (answer);        // * So return the answer like you said you would at Pt1
}

#ifndef _CALCULATION_H
#define _CALCULATION_H

void input_Func(void); //Input function of text.
float input_Area(void); //Input function of Area. **** FIXED NOW MATCHES THE .CPP file above
void input_Trap(void); //Input function of Trapezoid.  *** STILL BUGGED .CPP says it returns a float this still says void
float rectangle_Area (float , float); //Declaration for Rectangle Area.
float trapezoid_Area (float , float, float); //Declaration for Trapezoid Area.

#endif

#ifndef _CALCULATION_H
#define _CALCULATION_H

float RectangleArea (float width, float length);
float TrapezoidArea (float base1, float base2, float height); 

#endif

#include "Calculation.h"

//Calculation of Rectangle Area.
float RectangleArea(float width, float length)
{
	float Area_Rectange;
	Area_Rectange = width * length;
	return (Area_Rectange);
}

//Calculation of Trapezoid Area.
float TrapezoidArea(float base1, float base2, float height)
{
	float Area_Trapezoid;
	Area_Trapezoid = height * (base1 + base2) / 2;
	return (Area_Trapezoid);
}

#ifndef _INPUT_H
#define _INPUT_H

/* Asks user for menu choice up to given max value */
unsigned int MenuInput (char* prompt, unsigned int maxNum);

/* Asks user for a float within given range, with prompt text */
float GetFloatInput(char* prompt, float min, float max);

#endif

#include <iostream>
#include "input.h"

/* Asks user for menu choice up to given max value */
unsigned int MenuInput(char* prompt, unsigned int maxNum) {
	bool validFlag = false;
	unsigned int iResult;
	do {
		printf(prompt);												// Put prompt on screen	
		int err = scanf_s("%u", &iResult);							// Scan for a unsigned int and hold any error
		if ((err == 0) || (iResult > maxNum)) {						// Check value between 0 .. maxNum
			printf("Invalid menu choice try again\n");				// If value is invalid .. prompt that
		} else validFlag = true;									// Value is valid
		scanf_s("%*[^\n]");											// Make sure we dump any characters in buffer
	} while (validFlag == false);									// Loop until valid
	return (iResult);												// Return result
}

/* Asks user for a float within given range, with prompt text */
float GetFloatInput (char* prompt, float min, float max) {
	int err;
	float fResult;
	do {
		printf(prompt);												// Put prompt on screen	
		err = scanf_s("%f", &fResult);								// Scan for a float and hold any error
		if (err == 0) {												// Err = zero means entry is not a float
			printf("Entry is not a float try again\n");				// Prompt entry was not a float to screen
		} else {
			if (fResult < min) {									// Check entry is above minimum 
				printf("Re-enter value below minimum of %f\n", min);// Prompt that on screen
				err = 0;											// Set err to zero so we fail loop
			}
			if (fResult > max) {									// Check entry is below maximum 
				printf("Re-enter value above maximum of %f\n", max);// Prompt that on screen
				err = 0;											// Set err to zero so we fail loop
			}
		}
		scanf_s("%*[^\n]");											// Make sure we dump any characters in buffer
	} while (err == 0);												// Repeat until valid float
	return (fResult);												// Return the  result
} 

#include <iostream>
#include "calculation.h"
#include "input.h"
using namespace std;

float input_area (void) {
	float width = GetFloatInput("Enter the width of rectangle :", FLT_EPSILON, FLT_MAX);
	float height = GetFloatInput("Enter the length of rectangle :", FLT_EPSILON, FLT_MAX);
	return (RectangleArea(width, height));							//Function Call to Rectangle and return answer
}

float input_trap(void) {
	float base1 = GetFloatInput("Enter base1 of trapezoid : ", FLT_EPSILON, FLT_MAX);
	float base2 = GetFloatInput("Enter base2 of trapezoid : ", FLT_EPSILON, FLT_MAX);
	float height = GetFloatInput("Enter the height of trapezoid : ", FLT_EPSILON, FLT_MAX);
	return (TrapezoidArea(base1, base2, height));					//Function Call to Trapezoid and return answer
}

int main()
{
	bool exitFlag = false;
	/* Menu */
	while (!exitFlag){
		printf("\nMain Menu:\n");
		printf("	0) Exit program\n");
		printf("	1) Calculate area of rectangle\n");
		printf("	2) Calculate area of trapezoid\n");
		unsigned int choice = MenuInput("Enter your choice : ", 2);
		switch (choice) {
			case 1:
				printf("Area of rectangle = %f\n", input_area());
				break;
			case 2:
				printf("Area of trapezoid = %f\n", input_trap());
				break;	
			default:
				exitFlag = true;
		}
	};

	return 0;
}

#include <iostream>
#include <float.h>         // Added to define FLT_EPSILON & FLT_MAX
#include "calculation.h"
#include "input.h"
using namespace std;

#include <iostream>
#include "calculation.h"
#include "input.h"     // <----- GetFloatInput is defined in this include>
using namespace std;

int main(int argc, char**argv)

unsigned short iResult;   // Define iResult as unsigned short not unsigned int

int err = scanf_s("%hu", &iResult);   // Use %hu this should be error free on GCC

Hassan Syed1 wrote:

What is the main reason even till day-today there is no boundry condition set for C++.

#include <stdio.h>

// Link with library. Copy library to build path (debug / release),
//  specify full path here, or add path of libraray to project settings.
#pragma comment(lib, "fortran_library_name")

extern "C"
{
    // Functions exported by fortran_library_name and used in this program.
    // Note that function names may be all upper case.
    // The function name may be also exported with a leading underscore.
    // You can see the names in the DependencyWalker.
    void __stdcall some_fortran_lib_func1();

    // Another example with Fortran code
    // REAL*8 FUNCTION SOME_FORTRAN_LIB_FUNC2 (a, b)
    // REAL*8 a [VALUE]
    // REAL*8 b [REFERENCE]
    // b = SQRT(a)
    // SOME_FORTRAN_LIB_FUNC2 = a * a
    // END
    double __stdcall SOME_FORTRAN_LIB_FUNC2(double f, double *p);
}

int main()
{
    some_fortran_lib_func1();
    // Print result here if functions returns a value or modfies parameters 
    return 0;
}