Error expected expression before '{' token

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.

What is `res={a.num*b.num, a.den*b.den};` supposed to do? It's certainly not valid C. — Robert Harvey, Dec 07 '18 at 23:26
Is there some documentation or example code you saw that lead you to believe that line would work? — David Schwartz, Dec 07 '18 at 23:29
What/who lead you to belive that _typedefing_ a struct would be a good idea?, not a rhetorical question, I'm genuinely curious. — Jenny T-Type, Dec 07 '18 at 23:32
@JennyT-Type typedef'ing structs is very common and idiomatic in C. Why are you asking that question? — Barmar, Dec 07 '18 at 23:50
@Barmar Why?, curiosity?. I don't want to assume, I would do that (_typedefing_)to avoid declaring something like `struct mydata_type mysdata_var;` and go for `mydata_type mydata_var` saving me from typing the word `struct` again and some (tiny) disk space along the way, But then I would get into trouble if I forget I'm passing a struct instead of a union or an malloc'ed chunk, so if I would typedef I would have something like `typedef struct s_mydata_type {/* members */} s_mydata_type_t;` then, `typedef union u_myotherdata_type {/* mxmembers */} u_myotherdata_type_t` as reminders (cont). — Jenny T-Type, Dec 08 '18 at 13:56
(cont'd), but then, some programmers would chastise me about using prefixes (and suffixes) reserved for some future use by the C standard, So i found that refraining from typedefing saves me from using my data in an incorrect way (eg, assigning to members of an union as they were struct members -- not exactly trivial to pinpoint if compiled correctly), and from future concerns. With that being said, I sometimes typedef my structs and/or unions, if, for example, I'm going to use several variables of that type, or complex data structures from an specific type. — Jenny T-Type, Dec 08 '18 at 14:09

score 0 · Answer 1 · answered Dec 07 '18 at 23:53

0

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};

answered Dec 07 '18 at 23:53

mnistic

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AnT stands with Russia · Answer 2 · 2018-12-08T00:46:20.887

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 };
}

Error expected expression before '{' token

2 Answers2