The foreach Loop

When writing a for loop that accesses each element of an array once, you will end up writing code like this:

for(int i = 0; i < myArray.Length; i++)
{
    <do something with myArray[i]>;
}

In some cases, this code has unnecessary repetition: If you are not using the counter i for anything other than an array index, you still need to declare it, increment it, and write the condition with myArray.Length

The foreach loop is a shortcut that allows you to get rid of the counter variable and the loop condition. It has this syntax:

foreach(<type> <variableName> in <arrayName>)
{
    <do something with variable>
}

• The loop will repeat exactly as many times as there are elements in the array
• On each iteration of the loop, the variable will be assigned the next value from the array, in order
• The variable must be the same type as the array

For example, this loop accesses each element of homeworkGrades and computes their sum:

int sum = 0;
foreach(int grade in homeworkGrades)
{
    sum += grade;
}

• The variable grade is declared with type int since homeworkGrades is an array of int
• grade has a scope limited to the body of the loop, just like the counter variable i
• In successive iterations of the loop grade will have the value homeworkGrades[0], then homeworkGrades[1], and so on, through homeworkGrades[homeworkGrades.Length - 1]

A foreach loop is read-only with respect to the array: The loop’s variable cannot be used to change any elements of the array. This code will result in an error:

foreach(int grade in homeworkGrades)
{
    grade = int.Parse(Console.ReadLine());
}