Text Input/Output Functions in the C Language

When you start dealing with variables in C, you'll invariably stumble into the garden of I/O, or input/output. The computer's primary input device is the keyboard, and its primary output device is the monitor, and you need to know how to get C to recognize input and create create output.

Here is a quick summary of the C language text input and output functions that you can use to help read information from the keyboard and push information to the screen.

C Language Text I/O Functions

Function	Format	Description
atof()	[numvar = ]atof(string);	Converts a floating-point value found in string into a floating-point number, which can be stored in a variable, class="code">numvar, or used immediately. Requires the STDLIB.H header file to be included.
atoi()	[numvar = atoi](string);	Converts an integer value found in string into an integer, which can be stored in a variable, class="code">numvar, or used immediately. Requires the STDLIB.H header file to be included.
fflush(stdin)	fflush(stdin);	Removes characters from the input stream (keyboard).
fpurge(stdin)	fpurge(stdin);	Removes characters from the input stream (keyboard). This function must be used in Unix rather than class="code">fflush(stdin).
getchar()	[ch = ]getchar();	Reads a single character from the keyboard. The character is displayed and, optionally, stored in the char variable class="code">ch.
gets()	gets(string);	Reads a string of text from the keyboard (terminated by the Enter key). The text is stored in the variable class="code">string.
printf()	printf("format"[,var[,var...]]);	Displays formatted text according to the class="code">format string. Optional values or variables, var, can be specified to match placeholders or conversion characters in the format string.
putchar()	putchar(ch);	Displays the character ch on the screen, where ch is a single character (or escape code) in single quotes or the name of a char variable.
puts()	puts(string);	Displays the text string on the screen, where string is a literal string of text (enclosed in double quotes) or the name of a string variable.
scanf()	scanf("format",&var);	Reads information from the keyboard according to the conversion character in the format string. The information is then stored in the variable class="code">var, which must match the type of conversion character that's used (int, class="code">float, or char, for example).

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