Strings, Part I

Enough with numbers for a while. Strings of characters are another important type in C#.

A string in C# is a sequence of characters. For C# to recognize a literal sequence of characters, like hello, as a string, it must be enclosed in quotes " to delimit the string: "hello". Special cases are considered later in String Special Cases.

String Concatenation

Because everything in C# is typed, C# can give a special meaning to operators depending on the types involved, as we saw with /. We can operate on numbers with arithmetic operators, including +. With strings + has a completely different meaning. Look at the example:

Console.WriteLine("never" + "ending");

The plus operation with strings means concatenate the strings: join them together end to end.

C# is even a bit smarter. If you use a + with a string, presumably you are looking to produce a string, so even if the second operand to the + is not a string, it is automatically converted to a string representation before concatenating:

int x = 42;
string result;
result = "We get " + x;
Console.WriteLine(result);

You can chain concatenations. We could make a full sentence adding a period:

Console.WriteLine("We get " + x + ".");

Note to Python programmers: C# has no * multiplication operator for strings.

Four Copies Exercise

In a scratch program, declare and initialize a string variable. Write an expression that evaluates to four copies of the string, so it works no matter what value you gave your string.

Sum String Exercise

In a scratch program, declare and initialize two int variables, x and y. Then write an expression whose value is “x + y is 56”, except that 56 is replaced by the sum of x and y, and is not a literal, but calculated from the actual values of variables x and y (which do not need to add up to 56 specifically).

This has a trick to it.

Ints and Strings Added

In a scratch program, start with:

int x = 2;
int y = 3;

Think what each expression prints. Write one predicted response at a time, then test it, and put the right answer beside your answer if you were wrong:

x + "??" + y;
x + y + "??";
(x * y + "??");
"??" + x * y;
"??" + x + y;
x + "??" * y;

Can you explain the ones you got wrong, after looking at the actual answer? Precedence and operation order is important.