Input/output operation in C

The C standard library contains functions to support writing C programs:
Input support:
Output support:

Printing variables to the terminal output

The printf( ) function is used to print values of all primitive data types to the terminal

The syntax of the printf( ) function is as follows:

printf("formatString", value1, value2, ... );

The "formatString" can contain format conversion fields where value1, value2, etc will be placed

Commonly used format conversions

Formatting character	Meaning
`%d`	Print the (next) value as a signed decimal integer value
`%u`	Print the (next) value as a unsigned decimal integer value
`%ld`	Print the (next) value as a *long signed* decimal integer value**
`%lu`	Print the (next) value as a *long unsigned* decimal integer value**
`%f`	Print the (next) value as a floating point value
`%lf`	Print the (next) value as a double precision floating point value
`%o`	Print the (next) value as a octal based number
`%x`	Print the (next) value as a hexadecimal based number
`%p`	Print the address (pointer) as a hexadecimal based number
`%c`	Print the (next) value as a character (i.e., used the ASCII code)
`%s`	Print the (next) value as a string (will be explained much later)
`%%`	Print a % character

Commonly used conversion characters: %d (int), %f (float), %lf (double) and %s (string)

Example of using the printf( ) function

Example:

#include <stdio.h> int main( int argc, char* argv[] ) { int x; x = 65; // ASCII code for 'A' printf( "x = 65: %d, %u, %c\n", x, x, x); // Same values ! x = -1; printf( "x = -1: %d, %u, %c\n", x, x, x); } Output: x = 65: 65, 65, A x = -1: -1, 4294967295, ???

DEMO: /home/cs255001/demo/C/set1/printf.c

Reading input into variables from the keyboard

The scanf( ) function is used to read values from the keyboard into program variables of any primitive data types

The syntax of the scanf( ) function is as follows:

scanf("formatString", &var1, &var2, ... );

The "formatString" can contain format conversion fields to convert ASCII keyboard input into the correct internal representation for var1, var2, etc

Note: I will explain why you need to use the & symbol later !

Example of using the scanf( ) function

Example:

#include <stdio.h> int main( int argc, char* argv[] ) { int i; float x; printf( "Enter an integer value:"); scanf( "%d", &i ); // Must use %d to read int value printf( "i = %d\n", i); printf( "Enter a floating point value:"); scanf( "%f", &x ); // Must use %f to read float value printf( "x = %f\n", x); }

DEMO: /home/cs255001/demo/C/set1/scanf.c