Working with text

Strings

A std::string holds text. Join strings with +:

std::string color = "red";
std::string name = color + " ball";   // "red ball"

+ joins strings to strings, not numbers: "x = " + 0.5 won't compile. std::to_string(0.5) turns a double into text, but always with six decimals: "0.500000".

Strings come with member functions, called with a dot after the variable. color.size() is the number of characters, 3, and color[0] is its first character, 'r'. A single character goes in single quotes and has its own type, char.

std::format

Joining with + gets clumsy fast. std::format, from #include <format>, writes values into a pattern: each {} is replaced by the next value.

double x = 0.1234;
std::string msg = std::format("The {} ball is at x = {} m", color, x);
// The red ball is at x = 0.1234 m

Put a format after a colon inside the braces to control how a number looks. {:.2f} means "2 digits after the decimal point":

std::cout << std::format("x = {:.2f} m", x) << "\n";   // x = 0.12 m

You'll use this all the time to print positions and sensor readings without a wall of digits. Some later lessons use the older std::printf("x = %.2f m\n", x), which does the same job.

Your task

The starter has a ball's color and its position x in metres.

1. Print The word red has 3 letters, using color.size() for the 3.
2. Set label to text like red ball at x = 0.12 m, with x rounded to 2 decimal places. Use std::format.
3. Print label.

The grader reads color and x from the first two lines the starter prints, so keep those.