chapter4 io

15
Unit 4 Data Input and Output

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Page 1: Chapter4 Io

Unit 4Data Input and Output

Page 2: Chapter4 Io

Basic Functions

• A C program consists of one or more functions that contain a group of statements which perform a specific task.

• A C program must at least have one function: the function main.

• We can create our own function or use the functions that has been created in the library, in which case we have to include the appropriate header file (example: stdio.h).

Page 3: Chapter4 Io

• In this section, we will learn a few functions that are pre-defined in the header file stdio.h

• These functions are:– printf()– scanf()– getchar() & putchar()

• In addition to those functions, we will also learn about Format Specifier and Escape Sequence which are used with printf() and scanf().

Page 4: Chapter4 Io

printf()• Used to send data to the standard output (usually the

monitor) to be printed according to specific format.• General format:

– printf(“control string”, variables);• Control string is a combination of text, format specifier

and escape sequence.• Example:

– printf(“Thank you”);– printf (“Total sum is: %d\n”, global_var);

• %d is a format specifier• \n is an escape sequence

Page 5: Chapter4 Io

Format Specifier

No Format Specifier Output Type Output Example1 %d Signed decimal integer 762 %i Signed decimal integer 763 %o Unsigned octal integer 1344 %u Unsigned decimal integer 765 %x Unsigned hexadecimal (small letter) 9c6 %X Unsigned hexadecimal (capital letter) 9C7 %f Integer including decimal point 76.00008 %e Signed floating point (using e notation) 7.6000e+019 %E Signed floating point (using E notation) 7.6000E+01

10 %g The shorter between %f and %e 7611 %G The shorter between %f and %E 7612 %x Character ‘7’13 %s String ‘76'

Tells the printf() function the format of the output to be printed put.

Page 6: Chapter4 Io

Escape Sequence

Escape Sequence Effect\a Beep sound\b Backspace\f Formfeed (for printing)\n New line\r Carriage return\t Tab\v Vertical tab\\ Backslash\” “ sign\o Octal decimal\x Hexadecimal\O NULL

Escape sequence is used in the printf() function to do something tothe output.

Page 7: Chapter4 Io

scanf()

• Read data from the standard input device (usually keyboard) and store it in a variable.

• General format:– scanf(“Control string”, &variable);

• The general format is pretty much the same as printf() except that it passes the address of the variable (notice the & sign) instead of the variable itself to the second function argument.

• Example:

int age;printf(“Enter your age: “);scanf(“%d”, &age);

Page 8: Chapter4 Io

getchar() and putchar()

• getchar() - read a character from standard input• putchar() - write a character to standard output• Example:

#include <stdio.h>

void main(void){ char my_char; printf(“Please type a character: “); my_char = getchar(); printf(“\nYou have typed this character: “); putchar(my_char);}

Page 9: Chapter4 Io

9

String Input and Output

• To get input string:– gets ( )– scanf ( )– getchar ( )– getch ( )

• To produce string output– puts ( )– printf ( )– putchar ( )

• Note: program must include <stdio.h> file

Page 10: Chapter4 Io

10

• gets– a function that

will get a string of characters

• scanf– to input

individual words from a line of text

– blank spaces act as delimiters

#include <stdio.h>

int main(){

char s[80];printf("Please type in some words : ");gets(s);printf("You typed : %s\n", s);return 0;

}

#include <stdio.h>

int main(){

char word1[80], word2[80];printf("Please type TWO words : ");scanf("%s %s", &word1, &word2);printf("You typed : %s and %s\n", word1, word2);return 0;

}

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11

• getchar– to input a single

character– requires you to hit

enter.

• getch– to input a single

character– reads a key hit

without waiting for you to press enter.

#include <stdio.h>

int main(){

char c;printf("Please type ONE character : ");c=getchar();printf("You typed : %c\n", c);return 0;

}

#include <stdio.h>#include <conio.h>int main(){

char c;printf("Please type 1 character : ");c=getch();printf("You typed : %c\n", c);return 0;

}

Page 12: Chapter4 Io

12

• puts– outputs a string

as a whole

• printf– to output a string

• putchar– outputs

characters individually

#include <stdio.h>

int main(){

char a[80];puts("Type some words :");gets(a);puts(a);return 0;

}

#include <stdio.h>

int main(){

char a[80]="abcd";printf("%s\n", a);return 0;

}

#include <stdio.h>

int main(){

char letter;for (letter='A'; letter<='Z'; letter++)

putchar (letter);printf("\n");return 0;

}

Page 13: Chapter4 Io

13

String Input and Output (cont.)

Sample run:Enter a string:This is a test input of a string of characters.The string just entered is:This is a test input of a string of characters.

Page 14: Chapter4 Io

14

String Input and Output (cont.)

• A printf() function call can be used in place of a puts() function call– printf("%s\n",message);– puts(message);

• This correspondence between the output functions is not duplicated by the input functions scanf() and gets()– scanf() reads a set of characters up to either a

blank space or a newline character•scanf("%s",message); //No & is required

– gets() stops accepting characters only when a newline is detected

Page 15: Chapter4 Io

15

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

char a[20], b[20];

scanf("%s", a);fflush(stdin);gets(b);printf("%s\n", a);printf("%s\n", b);puts(b);

}

petaling jayapetaling jayapetalingpetaling jayapetaling jayaPress any key to continue

String Input and Output (cont.)