Variables and Arithmetic Expression

Notes from The C Programming Language

A decimal point in a constant indicates that it is floating point, however, so $5.0/9.0$ i not truncated because it is the ratio of two floating-point values.

printf specification

%3.0f says that a floating-point number is to be printed at least three characters wide, with no decimal point and no fraction dgits.
%6.1f describes another number that is to be printed at least six characters wide, with 1 digit after the decimal point.

Width and precision may be omitted from a specification: %6f says that the number is to be at least six characters wide; %.2f specifies two characters after the decimal point, but the width is not constrained.

%o for octal
%x for hexadecimal
%c for character
%s for character string
%% for % itself

for statement:

#include <stdio.h>

#define LOWER 0			/* lower limit of table */

#define UPPER 300		/* upper limit */

#define STEP  20		/* step size */

/* print Fahrenheit-Celsius table */

main()

{

	int fahr;

	for(fahr = LOWER; fahr <= UPPER; fahr = fahr + STEP)

		printf("%3d %6.1f\n", fahr, (5.0/9.0)*(fahr-32));

}

Character input and output

The standard library provides getchar() and putchar() for reading and writing one character at a time. getchar() reads the next input character from a text stream and returns that as its value:

c = getchar();

The function putchar prints a character each time:

putchar(c);

prints the contents of the integer variable c as a character, usually on the screen.

File copy: a program that copies its input to its output one character at a time:

#include <stdio.h>

/* copy input to output; 1st version */

main()

{

	int c;

	c = getchar();

	while(c != EOF)

	{

		putchar(c);

		c = getchar();

	}

}

EOF is defined in <stdio.h>.

As an expression has a value, which is the left hand side after the assignment, the code can be concise:

#include <stdio.h>

/* copy input to output; 2nd version */

main()

{

	int c;

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

		putchar(c);

}

The next program counts characters:

#include <stdio.h>

/* count characters in input; 1st version */

main()

{

	long nc; 

	nc = 0;

	while(getchar() != EOF)

		++nc;

	printf("%ld\n", nc);

}

long integers are at least 32-bits.

It may be possible to cope with even bigger numbers by using a double(double precision float).

#include <stdio.h>

/* count characters in input; 2nd version */

main()

{

	double nc;

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

		;

	printf("%.0f\n", nc);

}

printf uses %f for both float and double; %.0f suppresses printing of the decimal point and the fraction part, which is zero.

Counts lines:

#include <stdio.h>

/* count lines in input */

main()

{

	int c, nl;

	nl = 0;

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

	{

		if(c == '\n')

			++n1;

		printf("%d\n", nl);

	}

}

Word counting with loose definition that a word is any sequence of characters that does not contain blank, tab or newline. This is a bare-bones version of the UNIX program wc:

#include <stdio.h>

#define IN  1	/* inside a word */

#define OUT 0	/* outside a word*/

/* count lines, words, and characters in input*/

main()

{

	int c, nl, nw, nc, state;

	state = OUT;

	nl = nw = nc = 0;

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

	{

		++nc;

		if(c == '\n')

			++nl;

		if(c == ' ' || c == '\n' || c == '\t')

			state = OUT;

		else if(state == OUT)

		{

			state = IN;

			++nw;

		}

	}

	printf("%d %d %d\n", nl, nw, nc);

}

Every time the program encouters the first character of a word, it counts one more word.

Count the number of occurrences of each digit, of white space character(blank, tab, newline), and of all other characters:

#include <stdio.h>

/* count digits, white space, others */

main()

{

	int c, i, nwhite, nother;

	int ndigit[10];

	nwhite = nother = 0;

	for(i = 0; i < 10; ++i)

		ndigit[i] = 0;

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

	{

		if(c >= '0' && c <= '9')

			++ndigit[c - '0'];

		else if(c == ' ' || c == '\n' || c == '\t')

			++nwhite;

		else

			++nother;

		printf("digits =");

		for(i = 0; i < 10; ++i)

			printf(" %d", ndigit[i]);

		printf(", white space = %d, other = %d\n", nwhite, nother);

	}

}

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Variables and Arithmetic Expression

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