PRACTICE PROBLEM 2(24-1 to 31-1):COMPLEX NUMBERS

I had to forcefully format the output in the required manner.
For example it had to be +i and not +1i ..
So not much logic in this problem except for the calculation.
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#include<stdio.h>
void add(int,int,int,int);
void sub(int,int,int,int);
void mul(int,int,int,int);
int main()
{
  int a,b,c,d;
  scanf("%d\n%d\n%d\n%d",&a,&b,&c,&d);
  add(a,b,c,d);
  sub(a,b,c,d);
  mul(a,b,c,d);

  return 0;

}
void add(int a,int b,int c,int d)
{
  if(b+d==1)
  printf("%d+i\n",a+c);
  else if(b+d==-1)
  printf("%d-i\n",a+c);
  else if(b+d>=0)
  printf("%d+%di\n",a+c,b+d);
  else
  printf("%d%di\n",a+c,b+d);
}
void sub(int a,int b,int c,int d)
{
  if(b-d==1)
  printf("%d+i",a-c);
  else if(b-d==-1)
  printf("%d-i",a-c);
  else if(b-d>=0)
  printf("%d+%di\n",a-c,b-d);
  else
  printf("%d%di\n",a-c,b-d);
}
void mul(int a,int b,int c,int d)
{
  if(a*d+b*c==1)
  printf("%d+i",a*c-b*d);
  else if(a*d+b*c==-1)
  printf("%d-i",a*c-b*d);
  else if(a*d+b*c>=0)
  printf("%d+%di",a*c-b*d,a*d+b*c);
  else
  printf("%d%di",a*c-b*d,a*d+b*c);

}