Little program crashes after taking a input

Question

I'm absolutely new to C language and computer science. I'm still learning how to code. This down below is a little program I wrote which converts the height in cm to feet and inches, however, the terminal crashes after it takes the height_cm as an input. I thought for a long time but cannot figure out the reason behind it.

#include <stdio.h>
int main(void)
{
    float height_cm;
    float feet=(int)(height_cm/2.54)/12;
    float inch=(height_cm/2.54);

    while(height_cm > 0)
    {
        printf("Enter a height in centimeters(<=0 to quit): ");
        scanf("%.2f", &height_cm);
        printf("%.2f = %d feet, %.2f inches", height_cm,feet,inch);
    }
    printf("Bye");
    return 0;
 }

Answer 1

Your main problem: You are referencing a unassigned variable height_cm when you are calculating feet and inches . This is going to produced a undefined behavior because the value in that variable is a junk value. The below snipped of code addresses some of you other problems, such as using %.2f in scanf , and performs your desired logic.

#include <stdio.h>
int main(void)
{
    float height_cm; // Currently junk value
    int feet;        // Currently junk value
    float inch;      // Currently junk value

    // Keep calculating feet / inches as long as the entered hight is positive
    do {
        printf("Enter a height in centimeters(<=0 to quit): ");
        scanf("%f", &height_cm); // Can only use "%.2f for printf not scanf"
        feet=(int)(height_cm/2.54)/12;
        inch=(height_cm/2.54);

        // Output results
        printf("%.2f = %d feet, %.2f inches", height_cm,feet,inch);
    }
    while (height_cm > 0);

    printf("Bye");

    return 0;
 }

Answer 2

You're specifying %d for your feet variable which is quite clearly a float , though oddly it's a float based on a rounded value, so you could use int if you wanted.

Turn on warnings like -Wall to be alerted to simple mistakes like this.

You'll also want to check for uninitialized variables as these are the primary source of crashes.

You can't use while on a variable that isn't defined. You must define it first.

Consider restructuring:

float height_cm;

while (true)
{
    printf("Enter a height in centimeters(<=0 to quit): ");
    scanf("%.2f", &height_cm);

    if (height_cm > 0) {
      int feet = (height_cm/2.54)/12;
      float inch = (height_cm/2.54) % 12; // Don't forget to modulo

      printf("%.2f = %d feet, %.2f inches", height_cm,feet,inch);
    }
    else {
      break;
    }
}

Due to how you're asking for input and looping around it you'll want to conditionally break rather than express the break condition in the while itself.

Answer 3

As others have stated, you are checking height_cm before assigning it a value. You can make a simple change to execute the loop at least once prior to checking for 0 by replacing the while with a do ... while loop:

    #include <stdio.h>
    int main(void)
    {
    float height_cm;
    float feet=(int)(height_cm/2.54)/12;
    float inch=(height_cm/2.54);

    do 
        {
        printf("Enter a height in centimeters(<=0 to quit): ");
        scanf("%.2f", &height_cm);
        printf("%.2f = %d feet, %.2f inches", height_cm,feet,inch);
        } while(height_cm > 0);
    printf("Bye");
    return 0;
    }