CHAPTER 2 PART #3 INPUT - OUTPUT 1 st semester King Saud University College of Applied studies and Community Service Csc

Outlines  Using the I/O operation  Printf function  Scanf function  Common Programming Errors 2

Input/Output Operations  Input operation  an instruction that copies data from an input device into memory  Output operation  an instruction that displays information stored in memory to the output devices (such as the monitor screen) 3

Input/Output Functions  A C function that performs an input or output operation  A few functions that are pre-defined in the header file stdio.h such as :  printf()  scanf()  getchar() & putchar() 4

The printf function  Used to send data to the standard output (usually the monitor) to be printed according to specific format.  General format:  printf(“string literal”); A sequence of any number of characters surrounded by double quotation marks.  printf(“format string”, variables); Format string is a combination of text, conversion specifier and escape sequence. 5

The printf function  Example:  printf(“Thank you”);  printf (“Total sum is: %d\n”, sum); %d is a placeholder (conversion specifier) marks the display position for a type integer variable \n is an escape sequence moves the cursor to the new line 6 Example printf("That equals %fKilometers.\n",kms); function name format string placeholder newline escape sequence print list

Printf with \n example 7

A Simple C Program: Printing a Line of Text (Cont.)  One printf can print several lines by using additional newline characters as in Fig  Each time the \n (newline) escape sequence is encountered, output continues at the beginning of the next line. 8

A Simple C Program: Printing a Line of Text (Cont.) 9

Escape Sequence Effect \aBeep sound \bBackspace \fFormfeed (for printing) \nNew line \rCarriage return \tTab \vVertical tab \\Backslash \”“ sign \oOctal decimal \xHexadecimal \ONULL 10

Placeholder / Conversion Specifier printfscanf int%d float%f double%f%lf char%c string%s 11

Examples printf("Please enter the student's grades:"); Please enter the student's grades: printf("The class average is %f ",average); The class average is printf("The total area is %f and the total cost is %d S.R.",tarea,tcost); The total area is 60.2 and the total cost is 4530 S.R. printf("The student received an %c grade in the course.",grade); The student received an A grade in the course. 12

Examples (Continue) printf("The grade is %c%c", grade, gradesymb); The grade is A+ printf("I am the first line\n"); printf("\n I am the second line\n"); I am the first line I am the second line 13

Value Format Displayed Output 234 %4d %5d %1d %4d %2d %5d-234 Formatting Numbers in Program Output 14

Value Format Displayed Output %6.2f %6.2f %6.2f %6.2f %6.2f %6.2f Formatting Numbers in Program Output 15

Value Format Displayed Output %5.2f %3.2f %4.2f %.3f %.4f %4.2f Formatting Numbers in Program Output 16

The scanf function  Read data from the standard input device (usually keyboard) and store it in a variable.  General format:  scanf(“Format string”, &variable); 17

The scanf function  Example : int age; printf(“Enter your age: “); scanf(“%d”, &age);  Common Conversion Identifier used in printf and scanf functions. printfscanf int%d float%f double%f%lf char%c string%s 18

The scanf function  If you want the user to enter more than one value, you serialise the inputs.  Example: float height, weight; printf(“Please enter your height and weight:”); scanf(“%f%f”, &height, &weight); 19

Examples scanf("%i",&workhours); scanf("%c",&letter); scanf("%i",&student_ID); scanf("%f",&tot_score); scanf("%f",&temperature); scanf("%f",&working_hours); scanf("%i%c",&population,&firstinitial); 20

Simple C Program: Adding Two Integers 21

Simple C Program: Adding Two Integers 22

Common Programming Errors  Debugging  Process removing errors from a program  Three (3) kinds of errors :  Syntax Error a violation of the C grammar rules, detected during program translation (compilation). statement cannot be translated and program cannot be executed 23

Common Programming Errors cont…  Run-time errors An attempt to perform an invalid operation, detected during program execution. Occurs when the program directs the computer to perform an illegal operation, such as dividing a number by zero. The computer will stop executing the program, and displays a diagnostic message indicates the line where the error was detected 24

Common Programming Errors cont…  Logic Error/Design Error An error caused by following an incorrect algorithm Very difficult to detect - it does not cause run-time error and does not display message errors. The only sign of logic error – incorrect program output Can be detected by testing the program thoroughly, comparing its output to calculated results To prevent – carefully desk checking the algorithm and written program before you actually type it 25