1.#QNANO in output in C language?

Question

#include <stdio.h>

float diff_abs(float,float);

int main() {
  float x;
  float y;
  scanf("%f", &x);
  scanf("%f", &y);
  printf("%f\n", diff_abs(x,y));
  return 0;
}

float diff_abs(float a, float b) {
  float *pa = &a;
  float *pb = &b;
  float tmp = a;
  a = a-b;
  b = *pb-tmp;
  printf("%.2f\n", a);
  printf("%.2f\n", b);
}

Hello guys, i'm doing a C program which should keep in a variable a-b, and in b variable b-a. It's all ok, but if i run my code at the end of output, compiler shows me this message:

3.14
-2.71
5.85
-5.85
1.#QNAN0

what does means 1.#QNANO?

Answer 1

In this piece of code printf("%f\n", diff_abs(x,y)) you are telling the compiler to print a float type of variable which should be the return value of the function diff_abs. But in your function diff_abs you are not returning any value.

So %f which is waiting for a float, will not get any value and it will print #QNAN0 which means Not A Number. So you can change your code as follows:

In your main:

//printf("%f\n", diff_abs(x,y));   //comment this line
diff_abs(x,y);  //just call the function

In the function:

void diff_abs(float a, float b) {  //change the return value to void
  //float *pa = &a;   //you are not using this variable
  float *pb = &b;
  float tmp = a;
  a = a-b;
  b = *pb-tmp;
  printf("%.2f\n", a);
  printf("%.2f\n", b);
  return;
}