2.1 Data types and expressions  (Page 2/5)

• Input by using the scanf() function
• Output by using the printf() function

To use printf and scanf functions, it is required to declare the header<stdio.h>

The printf() function

The standard library function printf is used for formatted output. It makes the user input a string and an optional list of variables or strings to output. The variables and strings are output according to the specifications in the printf() function. Here is the general syntax of printf .

The list of arguments allow expressions, separated by commas.

The string is all-important because it specifies the type of each variable in the list and how you want it printed. The string is usually called the control string or the format string. The way that this works is that printf scans the string from left to right and prints on the screen any characters it encounters - except when it reaches a % character.

The % character is a signal that what follows it is a specification for how the next variable in the list of variables should be printed. printf uses this information to convert and format the value that was passed to the function by the variable and then moves on to process the rest of the control string and anymore variables it might specify.

For Example

only has a control string and, as this contains no % characters it results in Hello World being displayed and doesn't need to display any variable values. The specifier %d means convert the next value to a signed decimal integer and so:

will print Total = and then the value passed by total as a decimal integer.

The % Format Specifiers

The % specifiers that you can use are:

Formatting Your Output

The type conversion specifier only does what you ask of it - it convert a given bit pattern into a sequence of characters that a human can read. If you want to format the characters then you need to know a little more about the printf function's control string.

Each specifier can be preceded by a modifier which determines how the value will be printed. The most general modifier is of the form:

The flag can be any of

The width specifies the number of characters used in total to display the value and precision indicates the number of characters used after the decimal point.

For example,

%10.3f will display the float using ten characters with three digits after the decimal point. Notice that the ten characters includes the decimal point, and a - sign if there is one. If the value needs more space than the width specifies then the additional space is used - width specifies the smallest space that will be used to display the value.