The stdio library is a popular one for writing information. It can be used in both C and C++ programs. To use it in a C++ program, #include <cstdio>.
Use function printf (print-formatted), which takes a format string followed by zero or more values to be inserted into the format. The format can contain value designators, which start with %, and printf substitutes the n-th value parameter for the n-th value designator. For example, suppose that x is 25 and y is 500. Then
printf("x = %i and y = %i\n", x, y)
writes string "x = 25 and y = 500\n" to the standard
output.
Value designators include the following.
| %i | The value has type int. Show it as a (decimal) integer. (%i is the same as %d. The d stands for decimal.) |
| %5i |
Like %i, but use at least 5 characters by adding
spaces on the left-hand side as necessary.
(If the number needs more than 5 characters
then it will not be shortened.) Number 5 in
this example is called a field width.
All of the value designators allow a field width. |
| %−5i | Like %5i, but put the spaces on the right side instead of on the left side. |
| %li | Like %i, but the value has type long. Notice that this is %li, with a lower-case l. |
| %c | The value has type char. Show it as a single character. |
|
%f %10.2f |
Show a number of type float. %10.1f shows the number using a total of at least 10 characters, with 2 digits shown to the right of the decimal point. |
|
%lf %10.2lf |
Similar to %f, but the value has type double. The lower-case l stands for 'long', since type double is sometimes referred to as 'long float'. |
|
%10.2e %10.2le |
Like %f or %lf, but use E format, showing the value using scientific notation. The lower-case l stands for 'long'. |
| %s | The value is a null-terminated string. Show it as a string. |
| %p | The value is a pointer. Show it as a memory address in base 16, prefixed by 0x. A NULL pointer is shown as 0x0 or (null). |
| %*i |
If the field width is given by an asterisk, the width
is taken from a parameter. So this actually uses two
of the parameters after the format, the field width then
the integer to show. For example,
printf("%*i", n, x);
shows the value of integer x using at least n
total characters.
You can use this with any of the field designators, such as c, s and f. |
Statement
putchar(c);is equivalent to
printf("%c", c);
but putchar is much more efficient.
Statement
printf("My sister is named %s and she is %i years old\n", "Laura", 10);
writes
My sister is named Laura and she is 10 years oldBe sure not to forget to add \n if you want to end the line. Statements
printf("I am ");
printf("anxious to finish\n");
writes
I am anxious to finishAlso do not forget spaces. Statement
printf("%i%i\n", 25, 32);
writes
2532
Suppose that variable mass is an integer (type int). Write a printf statement that writes
This thing's mass is ... kilogramswhere the ... has been replaced by the value of mass. Write an end-of-line at the end of it. Answer
Repeat the previous question, but this time assume that variable mass has type double. Answer
Write a definition of procedure writeSpaces(n), which writes n spaces. Assume that n is at least 1. Answer