i/o in c + misc
DESCRIPTION
I/O in C + Misc. Lecture 13 7.2.2002. Input : movement of data into memory from the outside world. read operation Changes the value of the variable Output: movement of data from memory to outside world. write operation does not change value of memory. - PowerPoint PPT PresentationTRANSCRIPT
6.2..2001 Sudeshna Sarkar, IIT Kharagpur1
I/O in C + Misc
Lecture 137.2.2002.
6.2..2001 Sudeshna Sarkar, IIT Kharagpur2
Input : movement of data into memory from the outside world. read operation Changes the value of the variable
Output: movement of data from memory to outside world. write operation does not change value of memory
6.2..2001 Sudeshna Sarkar, IIT Kharagpur3
In C, input and output is handled by a set of standard library functions.
Conceptually, C performs all I/O on text streams. The standard input stream from the keyboard
is referred to as stdin. The standard output stream is referred to as
stdout,
6.2..2001 Sudeshna Sarkar, IIT Kharagpur4
Single character input : getchar
getchar reads a single character from stdin
char ch;
ch = getchar(); The getchar function accepts any
character types in including newline, blank, and tab.
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Single character output : putchar
putchar prints a single character to stdout
char ch;
. . .
putchar (ch) ;
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Example/* Read a character from the keyboard and output it in reverse case */
#include <stdio.h>
#include <ctype.h>
main()
{
char alpha;
printf (“\n Enter a alphabet (lowercase or uppercase): “);
alpha = getchar();
if (islower(alpha))
putchar (toupper(alpha));
else
putchar (tolower(alpha));
}
6.2..2001 Sudeshna Sarkar, IIT Kharagpur7
Display formatted output (printf)
printf (“Enter %d positive numbers:”, num1*2);
printf (“control string”, list of expressions) ; Control string gives the format of output. Expressions are what to output %d is a placeholder for an int value.
printf (“The %d-th character is %c\n”, i, ch);
% placeholders in format string match expressions in output list in number, order, type.
6.2..2001 Sudeshna Sarkar, IIT Kharagpur8
Read input : scanf
scanf (“control string”, &input list) ;
scanf(“%d”, &number);
scanf(“%d%lf”,&studentId, &grade); Input list variables must be preceded by an & % placeholders in the format must match
variables in the input list. one-for-one in number, order, and type.
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Whitespace
“Whitespace”: space ‘ ‘, tab ‘\t’, newline ‘\n’ Skipped by scanf for int (%d) and double
(%lf) user can type spaces before a number and
they are ignored. Not skipped for char input (%c)
each character typed, including spaces, is used
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Review: Mixed Mode ArithmeticWhat is 2 * 3.14 ?
The compiler implicitly (automatically) converts int to double when they occur together.
Generally in mixed expressions, the variable whose type has lower precision is promoted to the type of the variable with higher precision.int
unsigned int
unsigned long int
long int
float
double
long doublehigher precision
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double d;
int x=5, y=2;
double dx=5.0, dy=2.0;
d = x/y;
printf(“1. d =%f\n”, d);
d = dx/y;
printf(“2. d =%f\n”, d);
d = x/dy;
printf(“3. d =%f\n”, d);
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Assignment : mixed modefloat i, j;
i = 1.99; j = -1.99;
printf (“i = %d, j = %d\n”, i, j);
/* floating point numbers are truncated while converting to int */
Assignment rules: If the two operands in an assignment expression are of different
data types, then the value of the righthand operand will be converted to the type of the operand on the left.
A float value is truncated if assigned to an int. A double identifier is rounded if assigned to a float. An int may be altered if assigned to a short int or to a char.
6.2..2001 Sudeshna Sarkar, IIT Kharagpur13
Explicit conversions: case
(type) expression;
double avg = total/count;
double avg = (double)total / (double)count;
((int)(i+f)) % 4 /* i is int, f is float */
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Errors
Syntax : the required form of the program The C compiler catched these “syntax errors”
Semantics and logic: what the program means what you want it to do The C compiler cannot catch these kinds of
errors.
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Library functions: stdio.h
int getchar (void)
int printf(...)
int putchar(c)
int rand(void)
int scanf(...)
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Library functions: math.hdouble acos (double)
double asin (double)
double atan (double)
double ceil (double)
double floor (double)
double cos(double)
double exp(double)
double fabs (double)
double log (double)
double log10 (double)
double pow (double, double)
double sin (double)
double sinh (double)
double cosh (double)
double tan (double)
double tanh (double)
double sqrt(double)
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Library functions: ctype.hint isalnum (char)
int isalpha (char)
int isascii (char)
int isdigit (char)
int islower (char)
int ispunct (char)
int isspace (char)
int isupper (char)
int toascii (char)
int tolower (char)
int toupper (char)