# 10.4. for loops¶

The loops we have written so far have a number of elements in common. All of them start by initializing a variable; they have a test, or condition, that depends on that variable; and inside the loop they do something to that variable, like increment it.

This type of loop is so common that there is an alternate loop statement, called for, that expresses it more concisely. The general syntax looks like this:

for (INITIALIZER; CONDITION; INCREMENTOR) {
BODY
}


This statement is exactly equivalent to

INITIALIZER;
while (CONDITION) {
BODY
INCREMENTOR
}


except that it is more concise and, since it puts all the loop-related statements in one place, it is easier to read. For example:

int i;
for (i = 0; i < 4; i++) {
cout << count[i] << endl;
}


is equivalent to

int i = 0;
while (i < 4) {
cout << count[i] << endl;
i++;
}


Run the active code below, which uses a for loop.

Run the active code below, which uses a while loop.

Construct the <code>half_life()</code> function that prints the first num half lives of the initial amount.

Run the active code below, which uses a for loop with a negative change in the “INCREMENTOR”.