1. Chapter 3 Input and Output
C Programming for Scientists & Engineers with Applications
by Reddy & Ziegler

2. 3.1 Input and Output Functions
Formatted Input and Output Functions
Standard Input Function
Standard Output Function

3. Standard Input Function
For input from the keyboard:
scanf(“format control string”, &var1, &var2, ..., &varn); or
For input from an input data file:
fscanf(stdin, “format control string”, &var1, &var2,…, &varn);
Programming Rule: The addresses of the input variables must be specified in the scanf() function.

4. Reading Data From the Keyboard
scanf (“%f %lf”, &income, &expense);
Pass these auguments to scanf
Convert the first keyboard data to a float type value and store the value in memory cell reserved for the variable income.
Conversion specifications
Note that %lf is for a double value
The addresses of the variables, income and expense
Use the “address of” operator, &, to pass the addresses of variables to functions

5. Using scanf() for input
scanf(“ %f %lf ”, &income, &expense );
And then saved in a float
type variable income
And then saved in a double
type variable expense
Will be converted
to float type
using %f
Will be converted
to double type
using %lf
Double type variable
Address of double
type variable
First keyboard
input
Second keyboard
input

6. Operation of scanf function
Value expressed
as int or float
Keyboard
input
value
Value in correct
memory cell
scanf
scanf statement
In source code
Addresses of memory
cell and way to
store the value

7. Standard Output Function
For output to the monitor or printer:
printf(“format control string”, var1, var2, var3,…, varn); or
For output to an output data file
fprintf(stdout, “ format control string”, var1, var2, var3,…, varn);

8. Sample C Program 2.5.1 sample code
/*******************************************************/
/* */
/* THIS IS THE FIRST COMPLETE C PROGRAM */
/* */
#include <stdio.h>
int main() {
int x, y, sum;
x = 5;
y = 6;
sum = x + y;
printf("x = %d y = %d sum = %d\n", x, y, sum);
return 0; }

9. For input and output the format control specifications for the built-in data types are:
For data type int : %d
For data type float : %f
For data type double : %lf or %e
For data type char : %c
For data type character string : %s

10. 3.2 File Input and Output Declaration of File Pointers
open and close Statements
Input from a Data File
Output to a Data File

11. Declaration of File Pointers
A file pointer for input and output files must be declared. The declaration of the file pointers are as follows:
FILE *inptr, *outptr;
The word FILE must be in uppercase letters; you cannot use lowercase letters.
The file pointer name must be preceded by an asterisk(*).

12. Input and output data files
For input:
inptr = fopen(“inputfile.dat” , “r”);
For output:
outptr = fopen(“outputfile.dat” , “w”);

13. Close data files fclose(inptr); fclose(outptr);
There are several options other than “r” and “w” for file operations listed in the text.

14. Input from an input data file
fscanf(inptr , “format control string”, &var1, &var2, &var3, ……..,&varn);
Instead of scanf for standard input, use fscanf for input from a data file. The first parameter must be the input file pointer.

15. Reading Data From A File
What function is most commonly used to read data from a file?
fscanf(file_pointer, format_string, argument_list);
Read the content of the file by file_pointer according to the conversion specifications in format_string
The contents read are put into the addresses given by the argument_list.
fscanf(inptr, “%d %lf”, &kk, &xx);
The functions scanf and fscanf are closely related.

16. Reading Data From A File
What is a file pointer?
A file pointer is a variable whose memory cell contains an address, which gives the key to accessing the file stored on disk.
FILE *inptr;
What is the convention for naming file pointers?
The same as naming conventions for C identifiers

17. Reading Data From A File
What is FILE?
A type set up for holding information about disk files
C derived data type in the header file stdio.h, which must be included to use FILE
Use the data type FILE to declare a file_pointer and use this file_pointer to handle your file
FILE file_pointer actual file
FILE “L3_6.IN”; (Wrong!!)

18. Reading Data From A File
How to open and close the file?
Use the C library function fopen( ) to create a link between a disk file and a file pointer.
file_pointer = fopen(file_name, access_mode);
inptr = fopen(“C3_6.IN”, “r”);
“r” means the file is opened for reading in text mode.
Use fclose( ) function to close a file manually.
fclose(file_pointer);
Run source code

19. Source Code #include <stdio.h> void main(void) { double xx ;
int ii, kk;
FILE *inptr;
inptr = fopen ("C3_6.IN","r");
fscanf(inptr, "%d", &ii);
fscanf(inptr, "%d %lf", &kk, &xx);
fclose(inptr);
printf("ii = %5d\n kk = %5d\n xx = %9.3lf\n",ii, kk, xx); }

20. Output to an output data file
fprintf(outptr , “format control string”, var1, var2, var3, ……..,varn);
Instead of printf for standard output, use fprintf for output to a data file. The first parameter must be the output file pointer as shown

21. Writing Output to A File
Topics
Writing data to a file
Using the fprintf( ) function
Previous programs have displayed all their output on the screen.
May be convenient
Once the screen scrolls or cleans, the output is lost

22. Writing Output to A File
An output file,
Can have any acceptable file name
Must be linked with a file pointer before it’s used.
Must be open before it’s used
Should be closed after it’s used

23. Writing Output to A File
What function is used to write data to a file?
fprintf(file_pointer, format_string, argument_list)
The fprintf( ) function writes the values of argument_list using the given format_string to a file that is linked to the program with the file pointer of file_pointer.
fprintf(myfile, “week=%5d\n year=%5d\n”, week, year);
The function fprintf is closely related to printf (like fscanf being related to scanf)

24. Operations of fprintf Function
Call to fprintf in
source code
File pointer
Indicating disk file
My file
Variable
Value with
formatting
Disk file
indicated
by file pointer
%7.2lf
fprintf
Conversion
specification
Variable
names
income

25. Writing Output to A File
What function is used to open an output file and to create a link between the file pointer and file?
Before data can be written to an external file, the file must be opened using the fopen( ) function
file_pointer = fopen(file_name, access_mode);
myfile = fopen(“L3_8.OUT”, “w”);
Use the fclose( ) function to close an output file
Run source code

26. Writing Output to A File
#include <stdio.h>
void main(void) {
double income=123.45, expenses=987.65;
int week=7, year=1996;
FILE *myfile;
myfile = fopen("L3_8.OUT","w");
fprintf(myfile,"Week = %5d\n Year = %5d\n",week,year);
fprintf(myfile,"Income = %7.2lf\n Expenses = %8.3lf\n", income,expenses);
fclose(myfile); }

27. 3.3 Filed Width Specification
Input Field Width Specification
Output Field Width Specification

28. Field Width Specification
In the format control string, the field width for each of the control fields can be specified for both input and output.
The specification of field width to align the output data properly is very important, because the alignment increases the readability of output displayed on the monitor, printed, or written to a data file.

29. %nd for integers
%nd for integers, where n must be a numeric literal which specifies the format field width for locating integers to input.
Examples are as follows:
%7d %10d %12d
These specifications provide 7 spaces, 10 spaces, and 12 spaces, respectively, for three integer numbers.

30. %nf for real numbers
%nf for real numbers, n must be a numeric literal which specifies the number of total decimal digits to be input possibly including a leading sign and a decimal point.
%8f %10f
These specifications mean the decimal numbers with sign and decimal point are found within the next 8 and 10 positions

31. example
With the field width specification %8.2f, the spaces are allocated as follows:
2 spaces for the fractional digits
1 space for the decimal point
1 space for the sign
4 spaces for the whole digits

32. 3.4 Input and Output of Characters
Standard Input and Output
File Input and Output
Unformatted Input and Output

33. Input and Output of Characters
Characters are stored internally in a code such as ASCII.
The ASCII code for characters is presented in Appendix A.
Each character is allocated one byte of storage.
One byte of memory can hold decimal numbers in the range of 0 to 255.
Therefore one byte of storage is enough to store 256 different character codes.
Character variables are declared using the basic data type char

34. Standard input of characters
scanf(“%c%c%c”, &chr1, &chr2, &chr3); assume data is xyz
There are no blank spaces in XYZ because there are no blank spaces in the format control string in the input statement.
Notice that %c is the format control string for character data.

35. standard output of characters
printf(“%c %c %c”, chr1, chr2, chr3);
The output is as follows: X Y Z
If the format string is %d instead %c:
printf(“%d %d %d”, chr1, chr2, chr3);
The output is as follows:

36. Input from a data file FILE *inptr; char chr1, chr2, chr3, chr4;
inptr = fopen(“infile.dat”, “r”);
fscanf(inptr, “%c%c%c%c”, &chr1, &chr2, &chr3, &chr4);
The input data is as follows: 3 XY stored in memory as:

37. Output of character data to an output data file
FILE *outptr;
outptr = fopen(“outoutfile.dat”, “w”):
char chr1 = ‘3’, chr2 = ‘ ‘, chr3 = ‘X’, chr4 = ‘Y’;
fprintf(outptr, “%c%c%c%c”, chr1, chr2, chr3, chr4);
The output is as follows: 3 XY

38. 3.5 Sample Programs Conversion from Polar to Cartesian Coordinates
Cost of a Steel Cage
Convection Heat Transfer
Air Conditioners Sales Report
Wavelength of Electron