When I input my data the program is not able to detect my data and it doesnt give me the output

Question

#include <stdio.h>

void main (void)
{
  
    float m, v, kinetic_energy;
    
    
    
    printf("Enter mass and velocity: ", m, v);
    scanf("%.1f", &m);
    scanf("%.1f", &v);
    
    printf("With m = %.1f kg and v = %.1f m/s,\n", m, v);
        
    kinetic_energy = 1/2*m*v*v;
    
    printf("the kinetic energy is found to be %.2f J.", kinetic_energy);

    
}

When i run my programme i cant seem to get my output and instead the data shown is 0.0

Welcome to StackOverflow! Please take the [tour] to learn how this site works, and read "[ask]". Then come back and [edit] your question, adding your input, the actual output, and the expected outputs at least. — the busybee, May 01 '22 at 10:39
Note that `scanf("%.1f", &m);` is probably incorrect (MS VC doesn't like it). Anyway if the input has more than 1 decimal, it would be left in the buffer to be read by the next `scanf`. And if it has more, why should you worry? — Weather Vane, May 01 '22 at 10:52

score 1 · Answer 1 · edited May 03 '22 at 04:01

You are passing extra parameters to printf. scanf doesn't support format specifiers the way you have done it. Perhaps your goal is to accept floating point numbers only upto a certain precision, for which you can refer here but it is messy and I don't see a scenario where one needs to do it. Also, you should check the return value of scanf to see if your input has been read and assigned to variables. You can read more about it in its man page. It basically returns the number of values successfully read. I suspect you are using some old compiler like TurboC but you should learn to code as per the latest standards. As for why your answers are 0.0, the computation is being casted to int so you can either use 1.0/2*m*v*v or cast it explicity (float)1/2*m*v*v. Here is what the correct code would be like

#include <stdio.h>

int main(void)
{
  float m, v, kinetic_energy;

  printf("Enter mass and velocity: ");
  /* always validate EVERY user-input, especially numeric conversions */
  if (scanf ("%f", &m) != 1) {    /* validate input for m */
    fputs ("error: invalid floating point input.\n", stderr);
    return 1;
  }
  if (scanf ("%f", &v) != 1) {    /* ditto for v */
    fputs ("error: invalid floating point input.\n", stderr);
    return 1;
  }

  printf("With m = %0.1f kg and v = %0.1f m/s,\n", m, v);

  kinetic_energy = (float)1 / 2 * m * v * v;    /* compute energy */

  printf("the kinetic energy is found to be %0.2f J.", kinetic_energy);
  return 0;
}

PS: fputs here, is used to dump error messages, which should be kept separate from the general program output(stdout) to stderr as a good practice.

score 0 · Answer 2 · answered May 01 '22 at 10:48

Change void main (void) to int main(void).

Remove , m, v from printf("Enter mass and velocity: ", m, v);.

In the scanf calls, change %.1f to %f.

In kinetic_energy = 1/2*m*v*v;, 1/2 divides the int 1 by the int 2 and produces an int result which is truncated, so it is 0. Change the expression to use floating-point constants, not integer constants.

When I input my data the program is not able to detect my data and it doesnt give me the output

2 Answers2