lvalue required as left operand of assignment

Good evening. Why do I get the error with the ternary operator?

Code:

---


#define FOLD 40

int getLine(char* s, int lim)
{
  int i;
  char c;
  for(i = 0; i < lim - 1 && (c = getchar()) != EOF && c != '\n'; i++)
    (i % FOLD == 0)? s[i] = '\n' : s[i] = c;
 
  if(c == '\n')
    s[i++] = c;
 
  s[i] = '\0';
  return i;
}

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if I write

Code:

---

if(i % FOLD == 0)
 s[i] = '\n';
else
 s[i] = c;

---

I don't get the error. Why?

Quote:

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Originally Posted by thames

Good evening. Why do I get the error with the ternary operator?

Code:

---

    (i % FOLD == 0)? s[i] = '\n' : s[i] = c;

---

if I write

Code:

---

if(i % FOLD == 0)
 s[i] = '\n';
else
 s[i] = c;

---

I don't get the error. Why?

---

Because the ternary operator is an operator (that evaluates to a value), not a statement (like if is).

If you want to assign a newline to s[i] when i is a multiple of FOLD, and c otherwise, you can use s[i] = (i % FOLD) ? c : '\n'; or s[i] = (i % FOLD == 0) ? '\n' : c;
Note how the ternary operator is just an expression, not a statement? How it yields the value you assign?

That aside, do you realize that by doing that, you replace every FOLDth character by a newline, causing the replaced character to be lost?

Hint: only increment the index i in the loop definition. If you are at a folding point, append a space to the output array. Otherwise, read a character from input. If the character is EOF or newline, break out of the loop. Otherwise append it to the output array.

Many thanks.