chapter4 input and output

8/12/2019 Chapter4 Input and Output

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Unit 4Data Input and Output


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Basic Functions

A C program consists of one or more functions thatcontain a group of statements which perform a specifictask.

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

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


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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 usedwith printf() and scanf().


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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


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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+0110 %g The shorter between %f and %e 7611 %G The shorter between %f and %E 7612 %x Character 713 %s String 76'

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


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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.


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scanf()

Read data from the standard input device (usuallykeyboard) 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 (noticethe & sign) instead of the variable itself to the secondfunction argument.

Example:

int age; printf(Enter your age: );scanf %d, &a e ;


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getchar() and putchar()

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

#include

void main(void){

char my_char;

printf(Please type a character: ); my_char = getchar();printf(\nYou have typed this character: ); putchar(my_char);

}


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String Input and Output

To get input string: gets ( ) scanf ( ) getchar ( )

getch ( ) To produce string output

puts ( ) printf ( )

putchar ( ) Note: program must include file


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gets a function that

will get a stringof characters

scanf to input

individual wordsfrom a line oftext

blank spacesact as delimiters

#include

int main(){

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

}

#include

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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getchar to input a single

character requires you to hit

enter.

getch to input a single

character reads a key hit

without waiting foryou to press enter.

#include

int main(){

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

}

#include #include int main(){

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

}


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puts outputs a string as

a whole

printf to output a string

putchar outputs

charactersindividually

#include

int main(){

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

}

#include

int main(){

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

}

#include

int main(){

char letter;for (letter='A'; letter


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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.


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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 isnot duplicated by the input functions scanf() andgets()

scanf() reads a set of characters up to either ablank space or a newline character

scanf("%s",message); //No & isrequired

gets() stops accepting characters only when anewline is detected


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#include

#include void main (){

char a[20], b[20];

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

}

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