Trying to use scanf() to take in multiple variables

Question

So I've decided to add some programming skills to my repertoire, typically i've been an application support analyst with beginner to average SQL coding skills, but in today's climate I know I need to get better at automating simple tasks. So I bought a course in c programming (this is not for college credit, so by asking I'm not cheating). So far it's going quite well, but I've come against a problem, actually I decided to improve upon the challenge given to me and I can't seem to figure it out. Originally I was asked to create a small application that printed out the width, height, perimeter and area of a rectangle, with the width and the height hard-coded. That was simple to figure out. I decided to add an extra challenge and have the end user input the width and height of rectangle, but it's not working like I planned. I'm including my code and as well my output after compiling. I don't really want an answer as I would like to discover the solution myself, but if someone could point me to some documentation that would be much appreciated.

CODE:

#include <stdio.h>
#include <stdlib.h>
int main()

{
    double width;
    double height;
    double perimeter;
    double area;
    char newLine = '\n';
    printf("Please enter the width of your rectangle:");
    scanf("%f", &width);
    printf("Please enter the height of your rectangle:"); 
    scanf("%f", &height);
    perimeter = 2.0 * (height + width);
    area = (width * height);
    printf("%c",newLine);
    printf("The widith of the Rectangle is: %.2f centimeters %c",width, newLine);
    printf("The height of the rectangle is: %.2f centimeters %c",height, newLine);
    printf("The permimeter of the rectangle is: %.2f centimeters %c",perimeter, newLine);
    printf("The area of the rectangle is: %.2f centimeters %c",area, newLine);
    printf("%c",newLine);
    return 0;
}

OUTPUT:

[user@localhost.local]$ ./output/rectangle.a 
Please enter the width of your rectangle:15
Please enter the height of your rectangle:12

The widith of the Rectangle is: 0.00 centimeters 
The height of the rectangle is: 0.00 centimeters 
The permimeter of the rectangle is: 0.00 centimeters 
The area of the rectangle is: 0.00 centimeters

Did you compile with `-Wall`? If you did, the compiler would most likely have complained that you are using the wrong format specifier. `%f` are for reading/writing `float`. You have `double`, and should use `%lf`. — HAL9000, Oct 20 '19 at 20:50
I was using gcc, it didn't complain but I'll try that for sure. — Reuben deVries, Oct 20 '19 at 20:51
`-Wall` is not a compiler, it is an option that most compilers support for warning you when you are doing something suspect. It helps you miss when aiming at your foot. It is highly recommended for all c-programmers, beginners and experts alike. — HAL9000, Oct 20 '19 at 21:04
Just take note that no warnings will stop you from doing a semantically and syntactically valid facepalm, like only copying one byte with `memcpy`. — S.S. Anne, Oct 20 '19 at 21:24
Side note: There's a poor lesson that virtually all beginning C courses teach you, and that is: "If you want to read input from the user, use `scanf`". There is an important real-world lesson that almost no beginning C course teaches you, and that is: "Never use `scanf` for anything." `scanf` is square training wheels for beginning C programmers. Wean yourself off of it as soon as you can (see [here](https://stackoverflow.com/questions/58403537) for hints). — Steve Summit, Oct 20 '19 at 22:12

score 0 · Accepted Answer · answered Oct 20 '19 at 20:59

Your code is fine, the only problem is you using %f insted of %lf. %f is for float variable and %lf is for double variable.

The output of your program after fix:

Please enter the width of your rectangle:25
Please enter the height of your rectangle:12
The height of the rectangle is: 12.00 centimeters
The widith of the Rectangle is: 25.00 centimeters

The permimeter of the rectangle is: 74.00 centimeters
The area of the rectangle is: 300.00 centimeters

you can use this table to understand how to use each sort of data-types in c: https://www.geeksforgeeks.org/data-types-in-c/

Trying to use scanf() to take in multiple variables

1 Answers1