Standard input and output
Default input and output streams
Types of input and output data
Common input functions
Reference documentation about standard input functions and options:
- Simple character input functions (including the getchar() and getc() functions)
- Formatted input functions for all data types (including the scanf() function)
- Functions to classify characters (including the isalpha(), isdigit() and isspace() functions)
- Errors during standard input
- Description of formatted input options
- List of input formats by data type
- General syntax of formatted input formats
Character input
Classification of characters
The ctype.h header file contains some functions to identify different character types:
isalpha() returns 1 if the character is a letter
isdigit() returns 1 if the character is a number
isspace() returns 1 if the character is a space or newline
tolower() returns the input character in lowercase format
toupper() returns the input character in uppercase format
Text string input
Integer input
#include <stdio.h>
int main( void )
{
int number = 0;
while ( scanf( "%d", &number ) == 1 )
{
printf( "Found %d \n", number );
}
}
int main( void )
{
int number = 0;
while ( scanf( "%d", &number ) == 1 )
{
printf( "Found %d \n", number );
}
}
Floating point input
#include <stdio.h>
int main( void )
{
float number = 0;
while ( scanf( "%f", &number ) == 1 )
{
printf( "Found %f \n", number );
}
}
int main( void )
{
float number = 0;
while ( scanf( "%f", &number ) == 1 )
{
printf( "Found %f \n", number );
}
}
General input format
%[*][width]type
- The * is an optional flag to match and ignore that input data
- The return value of scanf() is the number of matching input variables
- When reading multiple input variables, a space between format codes skips any amount of leading spaces in the input data
Common output functions
Reference documentation about standard output functions and options:
- Simple output of characters or lines of text (including the putchar(), putc() and puts() function)
- Formatted output functions for all data types (including the printf() function)
- Description of formatted output options
- List of output formats by data type
- General syntax of formatted output formats
Character output
#include <stdio.h>
int main( void )
{
char code = 'a';
putchar( code );
putchar( '\n' );
code = 'b';
putc( code, stdout );
code = 'c';
printf( "%c\n", code );
}
int main( void )
{
char code = 'a';
putchar( code );
putchar( '\n' );
code = 'b';
putc( code, stdout );
code = 'c';
printf( "%c\n", code );
}
Text string output
Integer output
Floating point output
General output format
%[flags][width][.precision]type
Some useful flags:
– Left justify in field
+ Display positive or negative sign
0 Pad output with zeroes
Return value and escape characters
The return value of printf() is the number of characters printed.
Escape characters permit special characters to be printed:
\" double quotes
\' single quote
\? question mark
\n newline
\\ backslash
%% percentage sign
#include <stdio.h>
int main( void )
{
float code1 = 0.245722;
double code2 = 0.00451278;
int wordCount;
wordCount = printf( "%+7.4f \n", code1 * -1 );
printf( "Printed %d characters \n", wordCount );
printf( "%+7.4lf \n", code2 );
printf( "%10e \n", code1 );
printf( "%10E \n", code1 );
printf( "%10g \n", code1 );
printf( "%10G \n", code1 );
}
int main( void )
{
float code1 = 0.245722;
double code2 = 0.00451278;
int wordCount;
wordCount = printf( "%+7.4f \n", code1 * -1 );
printf( "Printed %d characters \n", wordCount );
printf( "%+7.4lf \n", code2 );
printf( "%10e \n", code1 );
printf( "%10E \n", code1 );
printf( "%10g \n", code1 );
printf( "%10G \n", code1 );
}