INTRODUCTION TO C++

C FORMATTED INPUT/OUTPUT

Dept. of Electronic Engineering, NCHU

Original slides are from http://sites.google.com/site/progntut/

Outline

printf and scanf

Streams (input and output) gets, puts

getchar, putchar

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Formatting output with printf

Syntax printf("format control string", other arguments);

Format control string could include Conversion specifications (begin with %)

Flags

Filed widths

Precisions

Literal characters

Other arguments: Each one corresponds to a conversion specification

optional

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Example of printf

int numDogs = 2, numCats = 1;

printf("I have %d dogs and %d cats\n", numDogs, numCats);

format control string argument

conversion specification

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Printing integers

Positive, negative, and zero

Integer conversion specification: %d: signed decimal integer

%i: signed decimal integer (different from %d in scanf)

%o: unsigned octal integer

%u: unsigned decimal integer

%x: unsigned hex integer (0-9, a-f)

%X: unsigned hex integer (0-9, A-F)

%h or %l: placed before any integer conversion specifier to indicate a short or long integer

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Example of printing integer

01 /* Fig 9.2: fig09_02.c*/

02 /* Using the integer conversion specifiers */

03 #include <stdio.h>

04

05 int main(void)

06 {

07 printf("%d\n", 455);

08 printf("%i\n", 455);

09 printf("%d\n", +455);

10 printf("%d\n", -455);

11 printf("%hd\n", 32000);

12 printf("%ld\n", 2000000000L);

13 printf("%o\n", 455);

14 printf("%u\n", 455);

15 printf("%u\n", -455);

16 printf("%x\n", 455);

17 printf("%X\n", 455);

18 return 0;

19 } /* end main */

455

455

455

-455

32000

2000000000L

707

455

4294955841

1c7

1C7

Output:

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Printing floating-point number

Floating point or exponential notation 153.2 = 1.532 x 102 = 1.532E2

Floating point conversion specification: %e or %E: Display floating-point in exponential notation

%f: Display floating-point in fixed-point notation

%g or %G: Display floating-point in either exponential or fixed-point based on the magnitude of the value

%L: Placed before any floating-point conversion specifier to indicate a long double

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Example of printing floating-point

01 /* Fig 9.4: fig09_04.c*/

02 /* Printing with floating-point conversion specifiers */

03 #include <stdio.h>

04

05 int main(void)

06 {

07 printf("%e\n", 1234567.89); 08 printf("%e\n", +1234567.89); 09 printf("%e\n", -1234567.89); 10 printf("%E\n", 1234567.89); 11 printf("%f\n", 1234567.89);

12 printf("%g\n", 1234567.89); 13 printf("%G\n", 1234567.89); 14

15 return 0;

16 } /* end main */

1.2345678e+006

1.2345678e+006

-1.2345678e+006

1.2345678E+006

1234567.890000

1.234567e+006

1.234567E+006

Output:

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Printing Strings and Characters

%c: Print character

Single quotes for character constant (‘z’, ‘a’, or ‘\n’)

Print the first character of a string

printf("%c“, “string”); // output: s

%s: Print string

Double quotes for strings (“z”, “string”)

Can not print characters

s

s \0

„s‟

“s”

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Example of printing strings

01 /* Fig 9.5: fig09_05.c*/

02 /* Printing string and characters */

03 #include <stdio.h>

04

05 int main(void)

06 {

07 char ch = 'a'; /* char */

08 char string[] = "This is a string."; /* char array */

09 const char *stringptr = "Also a string"; /* char pointer */

10

11 printf("%c\n", ch);

12 printf("%s\n", "This is a string."); 13 printf("%s\n", string); 14 printf("%s\n", stringptr); 15

16 return 0;

17 } /* end main */

a

This is a string.

This is a string.

Also a string

Output

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Other conversion specifiers

%p Display the address of a pointer value

%% Print a percent sign (%)

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Printing with field widths

Size of field in which data is printed

If the width is larger than data, default right justified If the field width is too small, it is increased to fit data

Minus sign occupies one character in the field

Integer width inserted between % and conversion specifier %4d: field width is 4

printf(“print %4d”, 23);

p r i n t 2 3

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Example of field widths

printf(“%4d\n”, 1); printf(“%4d\n”, 12); printf(“%4d\n”, 123); printf(“%4d\n”, 1234); printf(“%4d\n”, 12345);

printf(“%4d\n”, -1); printf(“%4d\n”, -12); printf(“%4d\n”, -123); printf(“%4d\n”, -1234); printf(“%4d\n”, -12345);

1111 1112 1123 1234 12345 11-1 1-12 -123 -1234 -12345

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Printing with precision

Usage format % + dot (.) + precision number + conversion specifies Example: %.4d, %.4f

Definition varies with data types For integer Minimal number of digits to print If data is too small, prefixed with zeros Example: printf(“%.4d\n”, 12); => ourput: 0012

For floating point Number of digits to appear after decimal Example: printf(“%.4f\n”, 12.34) => output: 12.3400

For string Maximum number of characters to be written from string

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Example of precision

int i = 123;

printf(“%.4d\n%.9d\n”, i, i);

double f = 1234.5678;

printf(“%.3f\n%.3e\n%.4g\n”, f, f, f,);

char s*+ = “happy birthday”;

printf(“%.11s\n”, s);

0123 000000123 1234.567 1.234e+003 1235 happy birth

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Flags

Placed right after (%)

Several flags may be combined

Flag Description

- Left justify the output

+ Display + in front of a positive value

(space) Display a space „ „ in front of a positive value

# Display 0 in front of an octal integer

Display 0x or 0X in front of a hex integer

0 Pad a field with leading zeros

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Example of flags

printf(“%5d students\n”, 100); printf(“%-5d students\n”, 100);

printf(“%05d students\n”, 100); printf(“%+d\n%d\n”, 100, 100);

printf(“% d\n%d\n”, 100, -100);

printf(“%#o\n”, 1427); printf(“%#x\n%#X\n”, 1427, 1427);

00100 students 10000 students 00100 students +100 100 100 -100 02623 0x593 0X593

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Escape sequences

Escape sequence Output

\‟ Single quote („)

\” Double quote (“)

\? Question mark (?)

\\ Backslash (\)

\a Bell

\b Backspace (Move the cursor back one position)

\f Move the cursor to the start of the next page

\n Move the cursor to the next line

\r Move the cursor to the beginning of the current line

\t Move the cursor to the next horizontal tab position

\v Move the cursor to the next vertical tab position

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Formatting output with scanf

Syntax scanf("format control string", &var1, &var2, …);

int a; scanf(“%d”, &a); // read integer

double f; scanf(“%lf”, &f); // read double floating point

char ch; scanf(“%c”, &ch); // read character

char s[10]; scanf(“%s”, s); // read string (should notice the size of string )

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