Flash cards
Review the key moves
What is the main idea behind C++ Array Size?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
___ myNumbers[5] = {10, 20, 30, 40, 50};Put the learning moves in the order that makes the concept easiest to apply.
Get the Size of an Array
To get the size of an array, you can use the sizeof() operator:
Example
int myNumbers[5] = {10, 20, 30, 40, 50};
cout << sizeof(myNumbers) ;Why did the result show 20 instead of 5 , when the array contains 5 elements?
It is because the sizeof() operator returns the size of a type in bytes .
You learned from the Data Types chapter that an int type is usually 4 bytes, so from the example above, 4 x 5 (4 bytes x 5 elements) = 20 bytes .
To find out how many elements an array has , you have to divide the size of the array by the size of the first element in the array:
Example
int myNumbers[5] = {10, 20, 30, 40, 50};
int getArrayLength = sizeof(myNumbers) / sizeof(myNumbers[0]) ;
cout << getArrayLength;Loop Through an Array with sizeof()
In the Arrays and Loops Chapter , we wrote the size of the array in the loop condition ( i < 5 ). This is not ideal, since it will only work for arrays of a specified size.
However, by using the sizeof() approach from the example above, we can now make loops that work for arrays of any size, which is more sustainable.
Instead of writing
int myNumbers[5] = {10, 20, 30, 40, 50};
for (int i = 0; i < 5; i++) {
cout << myNumbers[i] << "\n";
}Example
int myNumbers[5] = {10, 20, 30, 40, 50};
for (int i = 0; i < sizeof(myNumbers) / sizeof(myNumbers[0]); i++) {
cout << myNumbers[i] << "\n";
}It is better to write
Note that, in C++ version 11 (2011), you can also use the "for-each" loop , which is even cleaner and simpler:
Example
int myNumbers[5] = {10, 20, 30, 40, 50};
for (int num : myNumbers) {
cout << num << "\n";
}It is good to know the different ways to loop through an array, since you may encounter them all in different programs.