Error expected expression before '{' token [duplicate]

Question

typedef struct{
 int num, den;
} tfrac;

tfrac multf(tfrac a, tfrac b);

tfrac multf(tfrac a, tfrac b){
  tfrac res;
  res={a.num*b.num, a.den*b.den}; //The ERROR is here
  return res;
}

This program multiplies fractions. I don't know why I have an error in the function.

Answer 1

An initializer is a part of a declarator. So you can't declare your variable on one line and then assign values to it with an initializer on another line. Instead:

tfrac res={a.num*b.num, a.den*b.den};

Answer 2

The syntax you are using is not valid in C. You can get pretty close to this syntax in context of assignment operator by using a compound literal

tfrac multf(tfrac a, tfrac b)
{
  tfrac res;
  res = (tfrac) { a.num * b.num, a.den * b.den };
  return res;
}

Note the (tfrac) part before the {}.

But in your case you can simply use initialization instead of assignment

tfrac multf(tfrac a, tfrac b)
{
  tfrac res = { a.num * b.num, a.den * b.den };
  return res;
}

However, returning to compound literals again, if you prefer, you can use a compound literal to turn the whole thing into an one-liner

tfrac multf(tfrac a, tfrac b)
{
  return (tfrac) { a.num * b.num, a.den * b.den };
}