Programming Data Types

Question

I am trying to learn C and have come up with the following small program.

#include "stdafx.h"

void main()
{
    double height = 0;
    double weight = 0;
    double bmi = 0;

    printf("Please enter your height in metres\n");
    scanf_s("%f", &height);
    printf("\nPlease enter your weight in kilograms\n");
    scanf_s("%f", &weight);
    bmi = weight/(height * height);
    printf("\nYour Body Mass Index stands at %f\n", bmi);
    printf("\n\n");
    printf("Thank you for using this small program.  Press any key to exit");
    getchar();
    getchar();
}

The program compiles perfectly, however the answer returned by the program does not make sense. If I enter 1.8 for height and 80 for weight, the bmi is like 1.#NF00 which does not make sense.

What am I doing wrong?

Answer 1

When using scanf with a double, you must use the %lf specifier, as pointers are not promoted with scanf.

For more info, read the following question: Why does scanf() need "%lf" for doubles, when printf() is okay with just "%f"?

Answer 2

scanf (and scanf_s) format %f expects pointer to type float.

Simply change the type of your height and weight variables to float to fix this.

Answer 3

I think issue in scanf_s syntaxis, you ommited 3-rd argument, which is size of buffer in bytes. Try following:

scanf_s("%lf", &valueToGet, sizeof(double));