SCP 1103 Basic C Programming SEM 1 20102011

SCP 1103 Basic C Programming SEM 1 2010/2011 Week 6 Input & Output Operations

Formatted input / output • In C, data must be input to and output from a program through a file

Formatted input / output • Other then printf and scanf, C provides other function for input and output operation using library <stdio. h> & <conio. h> • Example: conio. h : clrscr stdio. h : scanf getch inport getchar feof

6. 1 Formatting Output

Formatting Output with printf – Precise output formatting • Conversion specifications: flags, field widths, precisions, etc. – Can perform • rounding, • aligning columns, • right/left justification, • inserting literal characters, • exponential format, • hexadecimal format, • fixed width and precision

Formatting Output with printf • Format of printf statement printf( format-control-string, otherarguments ); • Format control string: – describes output format – Ordinary characters - copy to output stream: – Example – printf(“this is an outputn”);

Formatting Output with printf • Format of printf statement printf( format-control-string, otherarguments ); • Other-arguments: – correspond to each conversion specification in format-control-string – Each specification begins with a percent sign (%), ends with conversion specifier

Formatting Output with printf • Format of printf statement

Formatting Output with printf • Format of printf statement – printf( format-control-string, otherarguments ); • Other-arguments: – Conversion specifications: leading with character ‘%’ – Format: %-w. p[d, f, c, s, …] • [-]: optional left justification, if exists • [w]: optional minimal width (wider if necessary). • [. ]: optional separates field w and p • [p]: optional maximum field width for a string precision of floating number • [d, f, c, s, …] : match to variable data type

Printing variable values • To print an integer: int degrees. F = 68; printf("The temperature is %d degrees. ", degrees. F); Specifier for “print an integer value” “Read value from this variable” Output: > The temperature is 68 degrees.

printf() • Format specifiers: – %c for single characters – %d for integers – %f for float/double (fractions): 1234. 56 – %g for float/double (scientific): 1. 23456 E+3 – %s for phrases or ‘strings’ (coming soon!)

Integer Conversion Specifier

Printing Character char a; printf("%c %d %x %0", a, a); A 65 41 101

Printing Integers • Integer – Whole number (no decimal point): 25, 0, -9 – Positive, negative, or zero – Only minus sign prints by default

Example 1 Output: 455 455 -455 3200000 707 455 4294966841 1 c 7 1 C 7

Printing Floating-Point Numbers • Floating Point Numbers – Have a decimal point (33. 5) – Exponential notation (computer's version of scientific notation) • 150. 3 is 1. 503 x 10² in scientific • 150. 3 is 1. 503 E+02 in exponential (E stands for exponent) • use e or E – f – print floating point with at least one digit to left of decimal – g (or G) - prints in f or e with no trailing zeros (1. 2300 becomes 1. 23)

Floating-point conversion specifiers

Example Program Output 1. 234568 e+006 -1. 234568 e+006 1. 234568 E+006 1234567. 890000 1. 23457 e+006 1. 23457 E+006

Printing Strings and Characters • c – Prints char argument – Cannot be used to print the first character of a string • s – Requires a pointer to char as an argument – Prints characters until NULL ('') encountered – Cannot print a char argument • Remember – Single quotes for character constants ('z') – Double quotes for strings "z" (which actually contains two characters, 'z' and '')

Other Conversion Specifiers • p – Displays pointer value (address) • n – Stores number of characters already output by current printf statement – Takes a pointer to an integer as an argument – Nothing printed by a %n specification – Every printf call returns a value • Number of characters output • Negative number if error occurs • % – Prints a percent sign – %%

Printing with Field Widths and Precisions • Field width – Size of field in which data is printed – If width larger than data, default right justified • If field width too small, increases to fit data • Minus sign uses one character position in field – Integer width inserted between % and conversion specifier – %4 d – field width of 4

Printing with Field Widths and Precisions • Precision – Meaning varies depending on data type – Integers (default 1) • Minimum number of digits to print – If data too small, prefixed with zeros – Floating point • Number of digits to appear after decimal (e and f) – For g – maximum number of significant digits – Strings • Maximum number of characters to be written from string – Format • Use a dot (. ) then precision number after % %. 3 f

Printing with Field Widths and Precisions • Field width and precision – Can both be specified • %width. precision %5. 3 f – Negative field width – left justified – Positive field width – right justified – Precision must be positive

Example printf("|%d|n", 987); printf("|%2 d|n", 987); printf("|%8 d|n", 987); printf("|%-8 d|n", 987); printf("|%0. 2 f|n", 9876. 54); printf("|%4. 2 f|n", 9876. 54); printf("|%3. 1 f|n", 9876. 54); printf("|%10. 3 e|n", 9876. 54); |987| |987 | |9876. 54| |9876. 5| | 9876. 540| | 9. 876 e+03|

Example ▪ ▪ ▪ 1234 12345 ▪ ▪-12 -12345

Example Using precision for integers 0873 000000873 Using precision for floating-point numbers 123. 945 1. 239 e+002

Printing Literals and Escape Sequences • Printing Literals – Most characters can be printed – Certain "problem" characters, such as the quotation mark " – Must be represented by escape sequences • Represented by a backslash followed by an escape character

Printing Escape Sequences

Exercise Week 6_1 • Identify the output of the following statements: 1. printf(“Ant’s Length: %2. 2 f sm", 2. 445 e-2); 2. printf("%c %d %u", 66, 0 x 50, 'C'); 3. printf("%-8 dn%6. 3 f %-6. 3 f", 4356, 1. 52);

6. 2 Formatted Input

Formatting Input with scanf • scanf – Input formatting (i. e. will scan formatted input from the keyboard – data entry purpose) – Capabilities • Input all types of data • Input specific characters • Skip specific characters

Formatting Input with scanf • Format – scanf(format-control-string, other-arguments); – Format-control-string • Describes formats of inputs – Other-arguments • Pointers to variables where input will be stored

Keyboard input: scanf() • Example - to read an integer: int num_students; scanf(" %d", &num_students); Specifier for “read an integer value” VERY IMPORTANT special symbol (&) ‘address of’ operator “Place value into this variable”

Formatting Input with scanf

Formatting Input with scanf

Formatting Input with scanf

Formatting Input with scanf

Example

Example

Example Enter a string: Sunday The input was: the character "S" and the string "unday" Program Output

Exercise Week 6_2 • Refer to Exercise 2 No. 1 in pg. 56. • What will be displayed if the following characters are entered in Program 6. 1 & 6. 2. Explain the program output with the following input. AV TY

6. 3 Simple Input Output

getchar() & putchar() • Use library stdio. h • getchar() - to read a single character from standard input - keyboard. – Pressing Enter causes the block of characters you typed to be made available to your program. • putchar() - to write a single character to standard output – output monitor. • Example: char huruf; huruf = getchar(); putchar (huruf+1); • Output with input ‘E’: EF

getch() & putch() • Use library conio. h • getch() - to read a single character from standard input keyboard. – The block of characters you typed available directly to your program. No need to press enter. – Does not echo the input. • putch() - to write a single character to standard output monitor. • Example: char huruf; huruf = getch(); putch (huruf+1); • Output with input ‘E’: F

getc() & putc() • Use library conio. h • getc() - to read a single character from standard input device – e. g. keyboard & file. – With stdin device type work similar with getchar(). • putc() - to write a single character to standard output device – e. g. monitor & file. • Example: char huruf; huruf = getc(stdin); putc (huruf, stdout);

gets() & puts() • Use library stdio. h • gets() - to read strings standard input device – Pressing Enter causes the strings you typed to be made available to your program. – The new line character will be stored as null (‘’) • puts() - to write string to standard output device. – To change null (‘’) to new line. • Example – input string “Dayang Norhayati” & store as: D a y a n g N o r h a y a t i

gets() & puts() #include <stdio. h> #include <conio. h> void main () { char nama[30]; printf("n. Enter Your Name please >>"); gets(nama); /*read string*/ printf("Good day "); puts(nama); /*print string*/ puts("It's your lucky day !!"); getch(); return 0; } Good day Dayang Norhayati It's your lucky day !!

Exercise Week 6_3 • Write C program to solve the flow chart.

6. 4 Hand Tracing a Program

Hand Tracing a Program • Hand trace a program: act as if you are the computer, executing a program: – step through and ‘execute’ each statement, one-by-one – record the contents of variables after statement execution, using a hand trace chart (table) • Useful to locate logic or mathematical errors

Hand Tracing a Program int main () { float num 1, num 2, num 3, avg; printf("Enter the first number> "); scanf("%f", &num 1); printf("Enter the second number> "); scanf("%f", &num 2); printf("Enter the third number> "); scanf("%f", &num 3); avg=(num 1+num 2+num 3)/3; printf("The average is %f", avg); getch(); return 0; } num 1 num 2 num 3 avg ? ? 1. 1 ? ? ? 1. 1 2. 2 3. 3 1. 1 The average is 1. 1

Exercise Week 6_4 • Trace the following programs void main(){ //Prog 6_41 int x, y, z; x =10; y = 17; z = x + y; y = y - x; printf ("x: %d y: %d z: %d”, x, y, z); x = y * z; z = x / 20; y = z % x; cout<<"nx: "<<x<< " y: “ <<y<<" z: "<<z; getch(); } void main(){//Prog 6_42 int n, m, x, y; m=10; n=m*2/(m+2); m%=n+2; cout <<"n: "<<n; cout <<"nm: "<<m; x=4; y=x*2+10%3 -1*x; x*=(y/m); cout<<"nx: "<< x; cout<<"ny: "<<y; getch(); }

6. 5 Introduction to File Input and Output

Introduction to File Input and Output • Can use files instead of keyboard, monitor screen for program input, output • Allows data to be retained between program runs • We use a file for three purposes: – reading data from it – writing or printing data into it – reading and writing data from/into it • These are called file modes

Introduction to File Input and Output • A file that is used for reading is called an input file (or data file) • A file that is used for writing is called an output file • We cannot read data from an output file & we cannot write data into an input file

Files: What is Needed • Steps: – Create the file – Open the file – Use the file (read from, write to, or both) – Close the file

Creating File • To cerate internal name • Creating an internal name means declaring a variable for the file - using pointer data type, FILE e. g. declaration of file variable

Opening Files • Create a link between file name (outside the program) and file stream object (inside the program) • Use the fopen member function: file_variable = fopen(“filename”, “file_mode”); • Filename may include drive, path info. • File mode tells the program how you intend to use the file –for reading or writing or both.

Opening Files – File Mode File mode Meaning r Open file for reading => an input file • If file exists, the file marker is positioned at beginning. & If file doesn’t exist errors returned. w Open file for writing => an output file • If file exists, it is emptied. & If file doesn’t, it is created. a Open file for appending = > an output file • If file exists, the file marker is positioned at end of file. & If file doesn’t exist, it is created. r+ Open an existing file for both reading & writing w+ Open a new file for both reading & writing a+ Open an existing file for both reading & writing & append at the end of the file

Using Files • Can use output file using fprintf: fprintf(file_variable, ”format string”, value_list); • Can use input file using fscanf: fscanf(file_variable, ”format string”, address_list); • fgetc & fputc: to read or print a character from file or to file. • fgets & fputs: to read or print strings from file or to file.

Closing Files • Use the close member function: fopen(file_variable); Don’t wait for operating system to close files at program end: – may be limit on number of open files – may be buffered output data waiting to send to file

Files - example #include <stdio. h> #define PI 3. 14159 int main(void) { double radius, area, circumference ; FILE *inp, *outp; inp = fopen("bulat. dat", "r"); outp = fopen("bulat. out", "w"); Create 2 files Open file to read Open file to write fscanf(inp, "%lf", &radius); area = PI*radius; circumference = 2*PI*radius; fprintf(outp, "Radius of a circle is %0. 2 fn", radius); fprintf(outp, "Area of the circle is %0. 2 fn", area); fprintf(outp, "circumference of the circle is %0. 2 f", circumference); fclose(inp); fclose(outp); return 0; } Close 2 files Use file

Closing Files - example Created by programmer Created automatically by program

Exercise Week 6_5 • Refer to Exercise 4 No. 1 -4 in pg. 58. • Solve the problem

Thank You Q&A