Character I/O

The Outside World

stdio.h: functions and constants for I/O

• Standard input and output

• File I/O

• Formatted

• Buffered

Most simple ones first:

int c;
c = getchar();
putchar(c);

cat for the Poor (1)

cat-poor.c

#include <stdio.h>

int main(void)
{
    int c;

    c = getchar();
    while (c != EOF) {
        putchar(c);
        c = getchar();
    }

    return 0;
}

cat for the Poor (2)

while (c != EOF)

EOF - End-of-File != - not equal

But ugly code duplication: getchar() called twice

while ((c = getchar()) != EOF) putchar(c);

An assignment is an expression ⟶ has a value ⟶ use that as condition Caution: operator precedence, braces!

More Examples …

long nc = 0; while (getchar() != EOF) ++nc;

Counting input characters ++: increment operator long: long integer (64 bit, mostly)

long nc; for (nc = 0; getchar() != EOF; ++nc);

Same with for loop and empty body Just more obscure

More Examples - if

Counting lines: \n terminates a line

int c, nl = 0;

while ((c = getchar()) != EOF)
    if (c == '\n')
        ++nl;

• if: alright

• ==: equality; but inappropriate for floating point numbers

• \n: character constant for newline (linefeed), ASCII 10 (0A)

if, Formally

if (expression)
    true-statement
else   // optional
    false-statement

Statement can be:

• Single statement (terminated with ‘;’)

• Multiple statements, grouped inside { ... }

Operators, Formally

==	Equality
!=	Inequality
&&	Boolean AND
||	Boolean OR
!	Boolean NOT