C Language Elements Preprocessor Directives

1. C Language Elements Preprocessor Directives # (sign for preprocessor directive commands) #include <standard header file> #include <stdio.h> #include <math> Standard header file (.h) Library

2. C Language Elements Preprocessor Directives Constant Macros • Program does not change their values # define Name value #define KILOS_PER_POUND 0.45359 • #define MILES_PER_KM 0.62137 • #define PI 3.141593

3. C Language Elements Function main • Every C program has main function • Has heading and body {} int main(void) { printf("This is a C program\n"); return (0); } The control returns back to OS Program was executed without error

4. C Language Elements Reserved Word • They have special meaning and can not be used for something else • All are lowercase some of them are: void case switch return for signed else long If do int while

5. C Language Elements Identifiers • Standard identifiers: scanf, printf • User-defined identifiers (should begin with a letter and only can contain digit or _ ) Invalid Valid 1rate rate1 int Rate1 joe’s x • Can be uppercase & lowercase • Meaningful name should be used for identifiers • They should not be redefined

6. C Language Elements Variable and data types • Variables are the name (identifiers) for memory cells that can be changed • It should start with a data type: int count; double x,y,z; char first_initial;

7. C Language Elements Data types • int: integer between -32767 to 32767 • double: for real numbers 3.14, 0.34 1.23e5, 1.23E5= 1.23 * 10 to the power 5 0.34e-4 = 0.000034 • char : for showing individual character ‘A’, ‘a’, ‘ ’,...

8. /* Convert the weight from pounds to kilograms */ comment #include <stdio.h> standard header file preprocessor #define KILOS_PER_POUND 0.45359 constant macro directive int reserved word main(void) { double pounds, variable kilos; printf(" Enter the weight in pounds"); standard identifier scanf(“%lf”, &pounds); special symbol kilos = pounds * KILOS_PER_POUND; printf(" That equals %f kilos. \n”, kilos); punctuation return (0); } special symbol

9. Executable Statements Data can be stored/changed in memory cells by • Assignment statement variable = expression; x= x + z / 6.9; x= -9; • Input operation that required #include <stdio.h>

10. Output Operation - printf printf( format string, printlist) • printf( “ Hi %c - your age is %d\n”, na,age); • printf (“It is 1th line\n”); printf (“\n and 2th line); • printf(“ Enter the weight in pounds”); scanf( “%lf” , &pounds); printf(“ %f pounds was entered”, pounds);

11. Input Operation-scanf scanf (format string, input list) • scanf (“%c%d”, &initial, &age); • & is using for each int, double and char variables (it means address of memory) • The order of placeholders correspond to the order of variables in the input list • For numbers the characters are scans until non-digits, blank or cr. For characters only first character before cr is considered

12. /* This program calculates ? */ #include <stdio.h> #define PI 3.14159 int main(void) { double r,a,c; scanf(“%lf”, r); a= PI * r * r; c= 2 * PI * r; printf( “? is %f cm^2. \n”, a); printf( “? is %f cm. \n”, c); return (0); }

13. Formating Values of Type int • printf ( “Result is: %3d meters”,… Examples: Value format display 234 %6d 234 234 %1d 234 -234 %6d -234 -234 %1d -234 234 %d 234

14. Formating Values of Type double • printf ( “Result is: %6.2f meters”,… Examples: Value format display -99.42 %6.1f -99.4 99.999 %6.2f 100.00 -.006 %8.5f -0.00600 -.003 %.3f -0.006 -3.15 %.1f -3.2 99.67 %f 99.67

15. #include <stdio.h> int main(void) { double x= 123.456; int y=12345; printf( “ %f %.3f %.1f \n”,x,x,x ); printf( “ %3d %5d %8d \n\n”,y,y,y ); return (0); } • 123.456 123.456 123.5 • 12345 12345 12345

16. Batch Mode Example: weightconvert <data >output include <stdio.h> #define KILOS_PER_POUND 0.45359 int main(void) { double pounds, kilos; scanf(“%lf”, &pounds); printf(“Weight in pounds is %.2f. \n“, pounds); kilos = pounds * KILOS_PER_POUND; printf(" That equals %f kilos. \n”, kilos); return (0); }

17. Program-controlled Input and Output files • File pointer variable include <stdio.h> #define KILOS_PER_POUND 0.45359 int main(void) { double pounds, kilos; FILE *inp, /* pointer to input file */ *outp; /* pointer to output file */

18. Os preparing the files for access /* open the input and output files */ inp = fopen (“a:weight.txt”, “r”); outp= fopen (“a:distance.out”, “w”); /* get the input from file */ fscanf(inp,“%lf”, &pounds); fprintf(outp, “Weight in pounds is %.2f. \n“, pounds);

19. kilos = pounds * KILOS_PER_POUND; /* Display the result in output file */ fprintf(output, “That equals %f kilos. \n”, kilos); /* Close files */ fclose(inp); fclose(outp); return (0); }

20. Common programming Errors Syntax Error Missing ; or variable definiation • double pounds instead of double pounds, kilos; Last comment is not closed • /* Close files instead of /* Close files */ Correct the errors in declaration part first

21. Runtime Errors scanf (“%lf” , &radius); scanf (“%c%c%c”, &a, &b, &c); instead of scanf (“%c%c%c”, &a, &b, &c); scanf (“%lf” , &radius); Input 50 ABC  a b c radius \n A B 50

22. Logic Errors • scanf( “%d%d” , a, b) => incorrect results • Deskchecking • Debugging