C Language Elements Preprocessor Directives # (sign for preprocessor directive commands) #include Standard header file (.h) Library

C Language Elements Preprocessor Directives Constant Macros Program does not change their values # define Name value #define KILOS_PER_POUND #define MILES_PER_KM #define PI

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

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

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

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;

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

/* Convert the weight from pounds to kilograms */ comment #include standard header file preprocessor #define KILOS_PER_POUND 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

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

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);

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

/* This program calculates ? */ #include #define PI 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); }

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

Formating Values of Type double printf ( “Result is: %6.2f meters”,… Examples: Value format display %6.1f %6.2f %8.5f %.3f %.1f %f 99.67

#include int main(void) { double x= ; int y=12345; printf( “ %f %.3f %.1f \n”,x,x,x ); printf( “ %3d %5d %8d \n\n”,y,y,y ); return (0); }  

Batch Mode Example: weightconvert output include #define KILOS_PER_POUND 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); }

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

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);

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); }

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

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

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