7.10. Increment and decrement operators¶
Incrementing and decrementing are such common operations that C++
provides special operators for them. The ++
operator adds one to the
current value of an int
, char
or double
, and –
subtracts
one. Neither operator works on string
s, and neither should be
used on bool
s.
Technically, it is legal to increment a variable and use it in an expression at the same time. For example, you might see something like:
cout << i++ << endl;
Looking at this, it is not clear whether the increment will take effect before or after the value is displayed. Because expressions like this tend to be confusing, I would discourage you from using them. In fact, to discourage you even more, I’m not going to tell you what the result is. If you really want to know, you can try it.
The active code demonstrates how using increment operators
with cout
statements can be confusing.
If you’re curious about this, feel free to search up about prefix and postfix increment operators. But for now, just avoid incrementing a variable and using it in an expression at the same time.
Using the increment operators, we can rewrite the letter-counter:
size_t index = 0;
while (index < fruit.length()) {
if (fruit[index] == 'a') {
count++;
}
index++;
}
The active code below adds increment operators to our old letter-counter.
It is a common error to write something like
index = index++; // WRONG!!
Unfortunately, this is syntactically legal, so the compiler will not
warn you. The effect of this statement is to leave the value of
index
unchanged. This is often a difficult bug to track down.
Warning
Remember, you can write index = index + 1;
, or you can write
index++;
, but you shouldn’t mix them.
def main() { count = count + 1; index++; count = count++; cout << x++ << endl; count--; }
- 5 4 3 2 1
- Notice that x is negative.
- -5 -4 -3 -2 -1
- Notice that the value of x is incremented before it is printed.
- -4 -3 -2 -1 0
- The value of x is incremented before it is printed so the first value printed is -4.
Q-4: What does the following code print?
1int x = -5;
2while (x < 0) {
3 x++;
4 cout << x << " ";
5}
Print every number from 1-10 in this format: “Number 1”. Each number should be on its own line.