I/O in C + Misc Lecture 13 7.2.2002. 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

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 Kharagpur

Conceptually, C performs all I/O on text streams. 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 Kharagpur

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. 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

Single character output : putchar putchar prints a single character to stdout char ch; . . . putchar (ch) ; 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

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 Kharagpur

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 Kharagpur

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. 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

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 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

Review: Mixed Mode Arithmetic What 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 double higher precision 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

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); 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

Assignment : mixed mode float 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 Kharagpur

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 */ 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

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. 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

Library functions: stdio.h int getchar (void) int printf(...) int putchar(c) int rand(void) int scanf(...) 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

Library functions: math.h double 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) 6.2..2001 Sudeshna Sarkar, IIT Kharagpur

Library functions: ctype.h int 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) 6.2..2001 Sudeshna Sarkar, IIT Kharagpur