Как мне заставить мое программирование на языке Си для функций работать должным образом

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У меня есть 2 проблемы.

1) I have 3 menu inputs as options 1, 2 and 3 that work fine with option 4 being the take a trip option. This option #4 allows you to say how many miles your trip will be. It operates as intended even letting me do multiple trips while it adds to a running total. I'm having a hard time in getting it to recognize the other options after I chose option 4. I see that if use return result at the end of option #4 if will allow me to use regular menu but it only allows me to run a running total twice when I go this route even with a loop. If I take away the return result on option #4 it will keep allowing the running total to run but won't allow me to access the other options on the menu.


2) Когда я могу получить доступ к другим опциям меню, когда у меня есть только возможность сделать running total на 2 номера, выбор другого варианта, чтобы сказать redo price of gas или miles per gallon, не сохраняет текущие общие данные, которые я имел от использования опции #4.

Вот мой код ниже...мы обязаны использовать функции и держать основные очень голые кости

#define _CRT_SECURE_NO_WARNINGS
#define PAUSE system("pause")
#define FLUSH myFlush()
#define CLS system("cls")
#include<stdio.h>
#include<stdlib.h>

//prototype functions here
void displayMenu(double choice);
void displayOutput(double pricePerGallon, double milesPerGallon, double getMilesBeginning, double milesDriven, double milesCurrent, double totalCost);
int getChoice(double milesBeginning, double pricePerGallon, double milesPerGallon);
double getMilesBeginning(double milesBeginning, double pricePerGallon, double milesPerGallon, double milesDriven, double milesCurrent, double totalCost);
double getMilesPerGallon(double milesPerGallon);
double getPricePerGallon(double pricePerGallon);
void myFlush();

main() {
	int choice;
	double milesBeginning = 0, pricePerGallon = 0, milesPerGallon = 0, milesCurrent = 0, milesDriven = 0, totalCost = 0;
	do {
		choice = getChoice(milesBeginning, pricePerGallon, milesPerGallon);
		switch (choice) {
		case 1:
			milesBeginning = getMilesBeginning(milesBeginning,pricePerGallon, milesPerGallon, milesDriven, milesCurrent, totalCost);
			break;
		case 2:
			pricePerGallon = getPricePerGallon(pricePerGallon);
			break;
		case 3:
			milesPerGallon = getMilesPerGallon(milesPerGallon);
			break;
		case 4:
			displayOutput(pricePerGallon, milesPerGallon, milesBeginning, milesCurrent, milesDriven, totalCost);
			break;
		case 5:
			break;
		default:
			printf("\nPlese pick a valid choice!!!\n\n");
			PAUSE;
			break;

		}//end switch 

	} while (choice != 5);

}//end of main

void displayMenu(double choice) {
	CLS;
	printf("\n1. Enter Beginning Mileage.\n");
	printf("2. Enter Price per Gallon.\n");
	printf("3. Enter Miles per Gallon.\n");
	printf("4. Take a trip.\n");
	printf("5. Quit the program.\n");
	printf("\n\n");
	printf("Enter your selection: ");
	
}//end displayMenu

void displayOutput(double pricePerGallon, double milesPerGallon, double milesBeginning, double milesDriven, double milesCurrent, double totalCost) {
	double result = 0;
	int choice = 0;

	if (milesBeginning <= 0 || pricePerGallon <= 0 || milesPerGallon <= 0) {
		printf("You must enter a positive value for choices 1, 2 & 3 before you proceed.\n"); FLUSH;
		return 0;
	}//end if

	do  {
		if (milesDriven <= 0) {
			CLS;
			printf("Please enter amount of miles traveled for this trip: ");
			scanf("%lf", &milesDriven); FLUSH;
			printf("You have traveled %.2lf miles for this trip.\n", milesDriven);

			printf("Your current mileage is %.2lf miles.\n", milesBeginning += milesDriven);
			printf("Your current trip cost $%.2lf.\n", (totalCost += (milesDriven / milesPerGallon) * pricePerGallon));
			
			PAUSE;
			
		}//end if
		/*else if (choice != 4) {
			displayMenu(choice);
			scanf("%c", &choice);
			CLS;
			return result;
		}*/

		


		do {
			displayMenu(choice);
			scanf("%c", &result);
			CLS;
			printf("Please enter amount of miles traveled for your next trip:  ");
			scanf("%lf", &milesDriven);
			printf("You have traveled %.2lf miles for this trip.\n", milesDriven);
			printf("Your mileage for this current trip is %.2lf miles.\n", milesDriven);
			printf("Your cost for this current trip is $%.2lf.\n", (milesDriven / milesPerGallon) * pricePerGallon);
			printf("Your Total mileage is %.2lf miles.\n", milesBeginning += milesDriven);
			printf("Your Total trip cost $%.2lf.\n", totalCost += (milesDriven / milesPerGallon) * pricePerGallon);
			PAUSE;
			displayMenu(choice);
			scanf("%c", &result);
			return choice;
			
		
		} while (choice != 5);//end of do loop
		

	} while (choice != 5);//end of do loop

	} //end of displayOutput

double getMilesBeginning(double milesBeginning, double pricePerGallon, double milesPerGallon, double milesDriven, double milesCurrent, double totalCost) {
	double result = milesBeginning;
	char choice; 
	CLS;
	printf("Your beginning mileage is %.2lf miles.\n", milesBeginning);
	printf("Press 'C' to change: ");
		scanf("%c", &choice); FLUSH;
		if (toupper(choice) != 'C')
			return result;
		else if (result > 0) {
			printf("You only get to enter a beginning number once.\n");
			printf("Please move on to other selections."); FLUSH;
		}
		else {
			printf("Please enter the beginning mileage:  ");
			scanf("%lf", &result);
			while (result <= 0) {
				printf("Please enter a positive number of beginning mileage.\n");
				printf("This program can't run until you do this.\n");
				printf("Please enter the beginning mileage:  ");
				scanf("%lf", &result); FLUSH;
			}//end while
		}//end else
		return result;
}//end getMileageBeginning

double getMilesPerGallon(double milesPerGallon) {
	double result = milesPerGallon;
	char choice;
	CLS;
	printf("Your Miles Per Gallon is %.2lf miles per gallon.\n", milesPerGallon);
	printf("Press 'C' to change: ");
	scanf("%c", &choice); FLUSH;
	if (toupper(choice) != 'C')
		return result;
	else {
		printf("Please enter the Miles Per Gallon:  ");
		scanf("%lf", &result); FLUSH;
		while (result <= 0) {
			printf("Please enter a positive Miles Per Gallon.\n");
			printf("This program can't run until you do this.\n");
			printf("Please enter the Miles Per Gallon:  ");
			scanf("%lf", &result); FLUSH;
		}//end while
	}//end else

	return result;
}//end get MilesPerGallon


double getPricePerGallon(double pricePerGallon) {
	double result = pricePerGallon;
	char choice;
	CLS;
	printf("Your Price Per Gallon is %.2lf per gallon.\n", pricePerGallon);
	printf("Press 'C' to change: ");
	scanf("%c", &choice); FLUSH;
	if (toupper(choice) != 'C')
		return result;
	else {
		printf("Please enter the Price Per Gallone:  ");
		scanf("%lf", &result); FLUSH; 
		while (result <= 0) {
			printf("Please enter a positive Price Per Gallon.\n");
			printf("This program can't run until you do this.\n");
			printf("Please enter the Price Per Gallon:  ");
			scanf("%lf", &result); FLUSH;
		}//end while
	}//end else
	return result;
}//end getPricePerGallon

int getChoice(double milesBeginning, double pricePerGallon, double milesPerGallon) {
	int result, choice = 0;
	//double pricePerGallon = 0, milesDriven = 0, milesPerGallon = 0, milesCurrent = 0, milesBeginning = 0;
	displayMenu(choice);
	scanf("%i", &result); FLUSH;

	return result;

}//end of getChoice

void myFlush() {    // this consumes all extra crap from the keyboard buffer
	while (getchar() != '\n');
} // end myFlush

Что я уже пробовал:

В течение последних нескольких дней я пытался изменить ситуацию во всех отношениях. Иногда у меня получается одно, а другое-нет. Любой совет очень ценится.

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