scanf format string requires argument of type

Question

Having lots of issues with my code, and have had people try explaining it to me but I still can't understand what I'm doing wrong... it all seems right in my head. As far as I understand, my char is not scanning correctly. I also have issues with returning values, and my "int * differs in levels of indirection from int". How can I fix my code? I'm completely lost.

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#define PAUSE system("pause")
#define CLS system("cls")
#define FLUSH flush()

// PROTOTYPE FUNCTIONS
void displayMenu();
void flush();
char getUserChoice();
int newSale(int *price, char *firstTime, char *veteran, char *student, char *lastDay);
int outputPrice(int carSales[], int *carsSold, int *avgCarPrice, int *totalRevenue);

// MAIN
main() {
    int carSales[500] = { 0 };
    int price = 0,  avgCarPrice = 0, totalRevenue = 0, carsSold = 0;
    char firstTime = 'n', veteran = 'n', student = 'n', lastDay = 'n';


    char userSelection;
    do {
        userSelection = getUserChoice();
        switch (userSelection) {
        case  'A': // ENTER A NEW SALE
            newSale(&price, &firstTime, &veteran, &student, &lastDay); // call function to ask questions
            printf("\nPRICE OF CAR: %i\n", price);
            carsSold++; // will add to +1 to the amount of cars sold
            carSales[carsSold] = price; // add the car to carSales array
            PAUSE;
            break;
        case  'B': // OUTPUT STATS
            outputPrice(&carSales[500], &carsSold, &avgCarPrice, &totalRevenue);
            PAUSE;
            break;
        case  'Q': //  Quit Program
            printf("Thanks....\n");
            break;
        default: // Invalid Selection
            printf("Invalid selection...try again!\n");
            PAUSE;
            break;
        } // end switch
    } while (userSelection != 'Q');
    PAUSE;
} // end of main

  // DISPLAY THE MENU
void displayMenu() {
    CLS;
    printf("========== MAIN MENU ==========\n");
    printf("A. ENTER NEW CAR\n");
    printf("B. OUTPUT STATS\n");
    printf("Q. QUIT\n");
    printf("Enter your choice: ");
} // end displayMenu

  // FLUSH
void flush() {
    while (getchar() != '\n');
} // end flush

  // GET THE USER CHOICE
char getUserChoice() {
    char result;
    displayMenu();
    scanf("%c", &result); FLUSH;
    result = toupper(result);
    return result;
} // end getUserChoice

int newSale(int *price, char *firstTime, char *veteran, char *student, char *lastDay) {

    // ASK QUESTIONS

    printf("What is the sticker price of the car?\n"); 
    scanf("%i", &price);

    printf("Are you a first time buyer? (y/n)\n");
    scanf("%s", firstTime);

    printf("Are you a veteran? (y/n)\n");
    scanf("%s", veteran);

    printf("Are you a student (y/n)\n");
    scanf("%s", student);

    printf("Is it the last day of the month? (y/n)\n");
    scanf("%s", lastDay);

    // CALCULATE PRICES

    if (*lastDay == 'y') { // car is discounted by 3% if user said yes
        *price = *price - (((int)(*price) * 3) / 10); // (int) is added to keep the cocmpiler from complaining due to an implicit cast to floating point. 
    }

    if (*firstTime == 'y') {  // if it's the user's first time buying, $100 is given in credit
        *price = *price - 100;
    }

    if (*student == 'y' && firstTime == 'y') { // car is discounted by $200 if user is a student and first time buyer- they also recieve the other discounts
        *price = *price - ((int)(*price) - 200);
    }

    if (*veteran == 'y') { // veterans recieve 2% off the final price of the car
        *price = *price - (((int)(*price) * 2) / 10);
    }

    return price;
}

int outputPrice(int carSales[ ], int *carsSold, int *avgCarPrice, int *totalRevenue) {
    printf("The total cars sold is: %i", carsSold); // Display the amount of cars sold

    for (int i = 0; i < 500; ++i) { // add all the prices in carSales 
        *totalRevenue = *totalRevenue + carSales[i];
    }

    printf("The Average car sold price: %i", avgCarPrice); // Display the avg price of the cars
    printf("Total revenue: %i", totalRevenue); // Display total revenue
    return;
}

Answer 1

First of all, the outputPrice function should have return type void rather than int; this gave me an error when I tried to compile your code originally.

Next, in the newSale function, the line

scanf("%i", &price);

should be changed to

scanf("%i", price);

because price is already a pointer. In the other four scanf calls, %s should be changed to `%c; e.g.

scanf("%s", firstTime);

should be changed to

scanf("%c", firstTime);

%s is the format specifier for a string; %c is for characters. Also note that the arguments still do not need to be referenced by prepending a & to their names, because they are also already pointers. The first line of the third if statement should be changed from

if (*student == 'y' && firstTime == 'y') {

to

if (*student == 'y' && *firstTime == 'y') {

Notice the & prepended to firstTime. This is necessary because firstTime is a pointer, not a character, and so comparing it to the character literal 'y' is going to yield incorrect results. However, firstTime is a pointer to a character, and so dereferencing it with * returns a character, which can then be compared to the character literal without a problem. The return statement also has a problem:

return price;

should be

return *price;

because the return type of the function is int, and price is an int pointer.

In the outputPrice function, the arguments in all of your printf statements need to be dereferenced. E.g.

printf("The total cars sold is: %i", carsSold);

should be

printf("The total cars sold is: %i", *carsSold);

because carsSold is an int pointer, not an int itself.

Also, main needs to be given a return type of int to avoid a compiler warning.