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Displaying Numerical Results

printf ( )

printf allows us to :

Evaluate arithmetic expressions.
Display their results.

Arguments : items passed to a function and are always placed within the function name parentheses .

Arguments must be separated from one another with commas, so the function knows where one argument ends and the next begins.

For example printf ("The sum of 3 and 12 is %d", 3+12);

The first argument is the message The sum of 3 and 12 is %d , and the second argument is the expression 3+12 .

The first argument passed to printf( ) must always be a message.

A message that includes a conversion control sequence , such as %d is termed as control string . A conversion control sequence begins with a % symbol and ends with a conversion character (d,c,f ,etc.) .

The percent sign % tells printf( ) to print a value at a place in the message where the % is located . The d , placed immediately after the % tells printf( ) that the value should be printed as an integer.

When printf( ) sees the conversion control sequence in its control string , it substitutes the value of the next argument in place of the conversion control sequence.

Thus the statement

printf ("The sum of 3 and 12 is %d .", 3+12);

causes the printout

The sum of 3 and 12 is 15.

Datatype	Conversion control sequence
int	%d
float	%f
long	%ld
double	%lf
char	%c

The %f ,%lf conversion control sequences causes printf( ) to display 6 digits to the right of the decimal place.

If the number < 6 decimal digits ,zeros are added to the number to fill the fractional part.
If the number > 6 digits , the fractional part is rounded to six decimal digits.

For example , the statement

printf ("The sum of %f and %f is %f",15.0, 18.0, 15.0 + 18.0);

causes the display

The sum of 15.000000 and 12.000000 is 18.000000

For example , the statement

printf ("The first letter of the alphabet is %c",'a');

causes the printout

The first letter of the alphabet is a

Formatted output

The format of numbers displayed by printf( ) can be controlled by field width specifiers included as part of conversion control sequence .

For example

printf ("The total of %2d and %3d is %4d",7,8,7+8)

causes the printout

The total of 7 and 8 is 15

The number 2 causes the first number to be print in a total field width of 2 space, in this case 1 blank space and followed by a number 7.

Example

#include<stdio.h>
void main( ) {

printf("Absence of field width specifiers\n");
printf("\n %d",3);
printf("\n %d",15);
printf("\n %d",142);
printf("\n ---");
printf("\n %d",3+15+142);

printf("\n\nUsing field width specifiers\n");
printf("\n %3d",3);
printf("\n %3d",15);
printf("\n %3d",142);
printf("\n ---");
printf("\n %3d",3+15+142);
}

OUTPUT

142

---

160

142

---

160

In formatting floating point numbers we can use 1 or 2 field width specifiers .

Example of 1 field width specifiier

printf (" %.3f ", 18.0) ;

causes the printout

18.000

When using 2 field width specifiers . The first specifiers determine the total display width ,including the decimal point . The second determine how many digits are printed to the right of the decimal point .

For all numbers (integers, floating point and double ), printf( ) ignores the specified field width if the total field width is too small and allocates enough space for the integer part of the number.

The fractional part of both floating point and double is always displayed with the number of specified digits .

If the fractional part contains fewer digits than specified , the number is padded with trailing zeros .
If the fractional part contains more digits than called for in the specifiers , the number is rounded to the indicated number of decimal places.

Specifier	Number	Display	Comments
\|%2d\|	3	\| 3\|	Number fits in field
\|%2d\|	24	\|24\|	Number fits in field
\|%2d\|	123	\|123\|	Field width ignored
\|%2d\|	2.5	Machine dependent ( 0 )
\|%5.2f\|	2.789	\| 2.79\|	rounded
\|%5.2f\|	12.1	\|12.10\|	add 0
\|%5.2f\|	123.123	\|123.12\|	truncated
\|%5.2f\|	123	Machine dependent

Format Modifiers

Left justification

use a minus sign

For example

printf("|%-10d",52);

|52 |

Explicit sign display

Normally the sign is only displayed for negative numbers . To force positive and sign to be displayed , a (+) format modifier must be used , for example:

printf("|%+10d|",12);

causes the display

| +12|

Format modifiers can be combined . For example , the conversion control sequence %+-10 would cause an integer number to both display its sign and be left justified . Since the order of the format modifiers is not critical ,we can use %-+10 in place of %+-10.

Other Number Bases

When outputting integers ,several display conversions are possible

Example

    #include<stdio.h>
    void main( ) {
    printf("\n The decimal (base 10) value of 18 is %d",18);
    printf("\n The octal (base 8) value of 15 is %o",15);
    printf("\n The hexadecimal (base 16) value of 10 is %x",10);
    }
would display

    The decimal (base 10) value of 18 is 18
    The octal (base 8) value of 15 is 17
    The hexadecimal (base 16) value of 10 is a

To designate an octal integer constant , the number must have a leading 0 . Hexadecimal numbers are denoted using a leading 0x.

Example

    #include<stdio.h>
    void main( ) {
    printf("\n The decimal of value of octal 025 is %d",025);
    printf("\n The decimal of value of hexadecimal 0x37 is %d",0x37);
    }
display:
    The decimal of value of octal 025 is 21
    The decimal of value of hexadecimal 0x37 is 55

To force both octal and hexadecimal to be printed with a leading 0 and 0x we must use the # .

For example :

printf (" The octal value of decimal 21 is %#o ",21);

The same display conversion can be used to display character .

Example

    #include<stdio.h>
    void main( ) {
    printf("\n The decimal of value of the letter %c is %d",'a','a');
    printf("\n The octal of value of the letter %c is %o",'a','a');
    printf("\n The hexadecimal of value of the letter %c is %x",'a','a');
    }

Display

    The decimal of value of the letter a is 97
    The octal of value of the letter a is 141
    The hexadecimal of value of the letter a is 61