### Log in from a computer to take this course

You'll need to log in from a computer to start Learn C. But you can practice or keep up your coding streak with the Codecademy Go app. Download the app to get started.

Learn

The main benefit of arrays is the ability to work with large amounts of data without assigning each piece of data its own variable name; therefore arrays usually contain many elements. To work with these elements, you will probably have to do something repeatedly. As you learned earlier in the course, a loop is used in order to execute repeated code. The technique of using a loop on an array is called “looping through the array.” Recall the two kinds of loops: a `for` loop and a `while` loop.

Let’s first take a look at how to loop through an array using a `while` loop. Consider the example of having an array consisting of 20 random integers and you wish to print its contents to the screen. Here’s how this is done with a `while` loop:

``````#include<stdio.h>

int main() {
int arr[] = {6, 9, 18, 37, 4, 23, 27, 16, 1, 30, 22, 7, 10, 25, 3, 2, 35, 11, 19, 28}; // Array
int i = 0; // Initialize index i to zero
while(i < 20){ // while loop
printf("%i\n", arr[i]); // Access element at index i in arr and print
i++; // Increment the index
}
}``````

In this piece of code, we have the 20 integer array `arr`. An index variable is declared and initialized outside of the loop. The loop runs for indices less than the size of the array (in this case, it is 20). The element at index `i` is printed along with a new line. Finally, the index is incremented by one.

This same process can be done using a `for` loop like so:

``````#include<stdio.h>

int main() {
int arr[] = {6, 9, 18, 37, 4, 23, 27, 16, 1, 30, 22, 7, 10, 25, 3, 2, 35, 11, 19, 28}; // Array
for(int i = 0; i < 20; i++){ // for loop
printf("%i\n", arr[i]); // Access element at index i in arr and print
}
}``````

### Instructions

1.

Loop through array `arr` and print each element on a separate line. The array contains 20 elements.

2.

Given the integer array `arr2`, fill up the array so that each element in the array is four plus the index of the element.

Example:

`arr[0] = 4`, `arr[1] = 5`, `arr[2] = 6`, etc.