Q.How does the monitor display 321 for statement

C has no built-in input/output; instead it uses library functions, declared in the header file stdio.h, to read data from the keyboard and display results on the screen. These divide into two groups.

Formatted I/O uses format specifiers to control the type and layout of the data:

• printf() prints formatted output. A specifier such as %d prints an integer, %f a real number, %c a character and %s a string. Width and precision can be added: %04d prints an integer in at least 4 columns padded with zeros, %5.3f prints a real number in 5 columns with 3 decimal places, and %e prints it in exponential form (e.g. 5.86280e-03).
• scanf() reads formatted input. Its general form is scanf("format string", &variable...); the ampersand & supplies the variable's address so the value can be stored there. …