C program treats an if statement as false when it is in fact true

Question

The following is a portion of code that I am writing for a homework assignment in my EEL4834 class. This is just for practice and not for a grade.

My problem is that the compiler is treating my if statement as false when it is true. I believe it to be true because I test the statement by printing the value of my variable in the else statement, and the value that is printed for my variable is the value that I am asking in the if statement.

The code...

#include <stdio.h>
#include <stdlib.h>

int main(void)
{  
    char a, b, c, d, box;
    float box1;

    printf("\nPlease enter the box type as a, b, c, or d:  ");
    scanf("\n%c", &box);

    if (box == a){  
        box1 = .05;
        printf("%f", box1);
        }
    else{
        printf("\n%c\n", box);
        }

    system("pause");
    return 0;
}

The output looks something like this...

Please enter a box type as a, b, c, or d: a

a
Press any key to continue . . .

The output is telling me that box is in fact a, but if box is a then why isn't the compiler treating the if statement as true? I omitted the if statements that include options for b, c, or d for simplicity.

I apologize if this is something stupid. I tried to use the search engine and anything relevant seemed much more complex that my issue. Thanks in advance for any help.

Answer 1

if (box == a){

compares the variable box against the variable a (which is undefined).

You should probably compare it against the character:

if (box == 'a') {

That also means you can get rid of the variables a, b, c and d, since they're not used for anything:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    char box;
    float box1;

    printf("\nPlease enter the box type as a, b, c, or d:  ");
    scanf("\n%c", &box);

    if (box == 'a') {
        box1 = .05;
        printf ("%f", box1);
    } else {
        printf("\n%c\n", box);
    }

    system("pause");
    return 0;
}

Answer 2

You're comparing against the variable named a, and not the literal character 'a'.

To understand what I mean, see a tutorial like this one