Introduction to Computing – B142L

Input and output

Academic year 2011/12



Objectives:

1. Standard data streams
2. Common output functions
3. Common input functions

Default input and output streams

Types of input and output data

Common output functions

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 ); }

References:

• Simple output of characters or lines of text   (including the putchar() and putc() functions)
• 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

Text string output

#include <stdio.h> int main( void ) { puts( "Step 1" ); printf( "%s", "Step 2" ); }

References:

• Simple output of characters or lines of text   (including the 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

Integer output

#include <stdio.h> int main( void ) { printf( "%d \n", 15 ); printf( "%i \n", 15 ); printf( "%u \n", 15 ); printf( "%u \n", -15 ); printf( "%x \n", 15 ); printf( "%X \n", 15 ); }

References:

• Simple output of characters or lines of text
• 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

Floating point output

#include <stdio.h> int main( void ) { float code1 = 0.245722; double code2 = 0.00451278; printf( "%.9f \n", code1 ); printf( "%.9lf \n", code2 ); printf( "%e \n", code1 ); printf( "%E \n", code1 ); printf( "%g \n", code1 ); printf( "%G \n", code1 ); }

References:

• Simple output of characters or lines of text
• 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

General output format

%[flags][width][.precision]type

Some useful flags:
– Left justify in field
+ Display positive or negative sign
0 Pad output with zeroes

#include <stdio.h> int main( void ) { float code1 = 0.245722; double code2 = 0.00451278; printf( "%+7.4f \n", code1 * -1 ); printf( "%+7.4lf \n", code2 ); printf( "%10e \n", code1 ); printf( "%10E \n", code1 ); printf( "%10g \n", code1 ); printf( "%10G \n", code1 ); }

References:

• Simple output of characters or lines of text
• Formatted output functions for all data types
• Description of formatted output options
• List of output formats by data type
• General syntax of formatted output formats

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 ); }

References:

• Simple output of characters or lines of text
• Formatted output functions for all data types
• Description of formatted output options
• List of output formats by data type
• General syntax of formatted output formats

Common input functions

Character input

#include <stdio.h> int main( void ) { char code; code = getchar(); printf( "Found %c \n", code ); code = getc( stdin ); printf( "Found %c \n", code ); scanf( "%c", &code ); printf( "Found %c \n", code ); }

References:

• 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
• Errors during standard input
• Description of formatted input options
• List of input formats by data type
• General syntax of formatted input formats

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

#include <stdio.h> #include <ctype.h> int main( void ) { char code; code = getchar(); printf( "Found %c \n", code ); if ( isalpha( code ) ) printf( "Alphabetical\n" ); if ( isdigit( code ) ) printf( "Numerical\n" ); }

References:

• 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

Text string input

#include <stdio.h> int main( void ) { char text[ 64 ] = { '\0' }; /* clear the string */ scanf( "%10s", text ); printf( "Found %s \n", text ); scanf( "%10c", text ); printf( "Found %s \n", text ); }Jack and Jill went up the hill to fetch a pail of water.

References:

• Simple character input functions
• Formatted input functions for all data types   (including the scanf() function)
• Functions to classify characters
• Errors during standard input
• Description of formatted input options
• List of input formats by data type
• General syntax of formatted input formats

Integer input

#include <stdio.h> int main( void ) { int number = 0; while ( scanf( "%d", &number ) == 1 ) { printf( "Found %d \n", number ); } }-10 0 11 21

References:

• Simple character input functions
• Formatted input functions for all data types   (including the scanf() function)
• Functions to classify characters
• Errors during standard input
• Description of formatted input options
• List of input formats by data type
• General syntax of formatted input formats

Floating point input

#include <stdio.h> int main( void ) { float number = 0; while ( scanf( "%f", &number ) == 1 ) { printf( "Found %f \n", number ); } }-10 0 10.0001 21.000001

References:

• Simple character input functions
• Formatted input functions for all data types   (including the scanf() function)
• Functions to classify characters
• Errors during standard input
• Description of formatted input options
• List of input formats by data type
• General syntax of formatted input formats

General input format and return value

%[*][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

#include <stdio.h> int main( void ) { int dd, mm, yy; if ( scanf( "%d%*c%d%*c%d", &dd, &mm, &yy ) == 3 ) printf( "Found %d-%d-%d", dd, mm, yy ); else printf( "Error with input" ); }21/04/99

References:

• Simple character input functions
• Formatted input functions for all data types   (including the scanf() function)
• Functions to classify characters
• Errors during standard input
• Description of formatted input options
• List of input formats by data type
• General syntax of formatted input formats

Review questions

---

Formatted input and output

Which is not a valid input and output format for C programs?

Float
Character
Line
Binary

Review questions

---

Formatted input and output

Which function below is equivalent to the C statement above?

printf() with %s
scanf() with %d
scanf() with %f
printf() with %t

Review questions

---

Formatted input and output

Use the string "Jack and Jill" as the input to the program below. What is the value of the variable key at the end of the program?

space
n
a
k