In C++ (especially with <iostream>), the ios class provides various functions to control the formatting of input and output. Here's what each option does:

width()
 Sets the field width (i.e., the minimum number of characters to be used for the next output).
✅ This is used to set the width.

precision()
 Sets the number of digits to display after the decimal point for floating-point values.

fill()
 Sets the character used to fill unused width space (default is space ' ').

setf()
 Sets format flags (e.g., std::ios::left, std::ios::right, std::ios::fixed, etc.).

✅ Correct Answer: (A) width()

std::cout.width(10); // sets width to 10 for the next output

std::cout << 123 << std::endl;