Question

#include <stdio.h>
#include <iostream>
using namespace std;

float cost, total;
bool loop(char item){
        switch (toupper(item)) {
            case 'A':
                cost = 4.25;        
                return true;
            case 'B':
                cost = 5.57;
                return true;
            case 'C':
                cost = 5.25;
                return true;
            case 'D':
                cost = 3.75;
                return true;
            case 'T':
                return false;
        }
        return true;
}

int main(){
        char item;
        do {
            printf("\nEnter Item Ordered [A/B/C/D] or T to calculate total:");
            scanf("%c", &item);
            total = total + cost;
        } while (loop(item)); 
        printf("Total Cost: $%f\n", total);
}

Let me output the process:

$ ./Case3.o 

Enter Item Ordered [A/B/C/D] or T to calculate total:a

Enter Item Ordered [A/B/C/D] or T to calculate total:
Enter Item Ordered [A/B/C/D] or T to calculate total:b

Enter Item Ordered [A/B/C/D] or T to calculate total:
Enter Item Ordered [A/B/C/D] or T to calculate total:a

Enter Item Ordered [A/B/C/D] or T to calculate total:
Enter Item Ordered [A/B/C/D] or T to calculate total:t
Total Cost: $28.139999

Why is it after the first printf its printing the printf twice but skipping me from input the first time. then how is it calculating 5.24+5.57+5.24 to equal 28.14?

Answer 1

As others have mentioned, When you press Enter, two characters get inputted, the character you enter + the newline, You need to account for both of these.

Possible solutions are:

Approach 1: The C way

 scanf(" %c", &item);
       ^^^

Add a space here, or the better approach,

Approach 2: The C++ way

simply use the C++ way of getting input from user.

cin >> item;

Why the result is Undefined?
Because you did not initialize the variable total, This results in Undefined Behavior giving you unexpected output.
total is a global so it will be Default Initialized to 0.0.
Real reason for Undefined result is in @Mystical’s answer.