What is wrong with my code? using structs and fprintf

I am working on a function for my project that formats the output of complex(imaginary) numbers, but when I run it, its not being formatted as i thought it would be.
the struct being used is:

Code:

typedef struct {
  double re;
  double im;
} complex;

And I am unable to change the type of re and im in the struct
the function i have written for this so far is:

Code:

void output_complex(FILE *outf,complex z)
{
   if(z.im == 0)
   {
      fprintf(outf,"%f", z.re);
   }
   if(z.re == 0)
   {
      if(z.im == 1)
      {
	 fprintf(outf,"i"); 
      }
      fprintf(outf,"%fi", z.im);
   }
    if(z.im == 1)
   {
      fprintf(outf,"%f + i", z.re);
   }
   if(z.im < 0)
   {
      if(z.im == -1)
      {
	 fprintf(outf,"%f - i", z.re);
      }
      z.im *= -1;  
      fprintf(outf,"%f - %fi", z.re, z.im);
   }
   fprintf(outf,"%f + %fi", z.re, z.im);
}

and there is this program that checks to see if the expected output is the same as the output of the function and this is what I got when I ran it for this function:
Output Function Errors:
expected: 1 + 2i
actual: 1.000000 + 2.000000i
expected: 3
actual: 3.0000003.000000 + 0.000000i
expected: 4i
actual: 4.000000i0.000000 + 4.000000
expected: i
actual:
expected: -2 + i
actual: i1.000000i0.000000 + i0.0000
expected: 4 - 2i
actual: 0 + 1.000000i
expected: 3 + 2i
actual: -2.000000 + i-2.000000 + 1.0
expected: 2 - i
actual: 0000i

what am I doing wrong?

Moved to duplicate thread: What is wrong with my code? using structs and fprintf.

Mods, feel free to close this one.

Also, you should check out string formatting characters, and how to set limits on them.Wikipedia's prinf page is a good place to start.