A Little C Primer/C Quick Reference

This section contains a sample program to give syntax examples for fundamental C statements, followed by a list of library routines. This list is very terse and simply provides reminders. If more details are needed, please refer to the previous chapters. /* sample.c: a silly program to give syntax examples. */ #include <stdio.h> /* Include header file for console I/O. */ int f1( int p ); /* Function prototypes. */ long f2( void ); long g; /* Global variable. */ void main( int argc, char *argv[] ) { float f; /* Declare variables. */ int ctr; extern long g; printf( "Arguments:\n\n" ); for( ctr = 0; ctr < argc; ctr++ ) { puts( argv[ctr] ); } printf( "\nFunction 1:\n\n" ); ctr = 0; while( ctr < 5 ) { printf( "%d\n", f1( ctr++ ) ); } printf( "\nFunction 2:\n\n" ); ctr = 0; do { g = ctr++; printf( "%d\n", f2( ) ); } while( ctr < 5 ); exit( 0 ); } int f1( int p ) { return( ( p < 3 ) ? p : p p ); } long f2( void ) { extern long g; return( g g ); } Console I/O -- #include <stdio.h>: int printf( char *s, <varlist> ) > 0 // Print formatted string to stdout. int scanf( char *s, *<varlist> ) != EOF // Read formatted data from stdin. int putchar( int ch ) // Print a character to stdout. int getchar() != EOF // Read a character from stdin. int puts( char *s ) // Print string to stdout, add \n. char *gets() != NULL // Read line from stdin (no \n). PC console routines -- #include <conio.h>: int getch() != 0 // Get a character from the keyboard (no Enter). int getche() != 0 // Get a character from the keyboard and echo it. int kbhit() != 0 // Check to see if a key has been pressed. Format codes: %h // short int (scanf() only) %d // decimal integer %ld // long decimal integer %c // character %s // string %e // exponential floating-point %f // decimal floating-point %g // use %e or %f, whichever is shorter (printf() only) %u // unsigned decimal integer %o // unsigned octal integer %x // unsigned hex integer %10d // 10-character field width. %-10d // Left-justified field. %6.3f // 6-character field width, three digits of precision. '\0NN' // character code in octal. '\xNN' // character code in hex. '\0' // null character. File-I/O -- #include <stdio.h>: FILE *fopen( char *f, char *mode ) != NULL // Create or open file. int fclose( FILE *f ) // Close a file. rewind( FILE *f ) // Rewind. rename( char *old, char *new ) // Rename a file. remove( char *name ) // Delete a file. fseek( FILE *f, long offset, int origin) == 0 // Seek. fprintf( FILE *f, char *fmt, <varlist> ) > 0 // Formatted write. fscanf( FILE *f, char *fmt, &<varlist> ) != EOF // Formatted read. fwrite( void *b, size_t s, size_t c, FILE *f ) > 0 // Unformatted write. fread( void *b, size_t s, size_t c, FILE *f ) > 0 // Unformatted read. putc( int c, FILE *f ) // Write character. int getc( FILE *f ) != EOF // Read character. fputs( char *s, FILE *f ) // Write a string. fgets( char *s, int max, FILE *f) != NULL // Read a string. sprintf( char *b, char *fmt, <varlist> ) // Print into string. sscanf( char *b, char *fmt, &<varlist> ) > 0 // Scan string. File modes: r // Open for reading. w // Open and wipe (or create) for writing. a // Append -- open (or create) to write to end of file. r+ // Open a file for reading and writing. w+ // Open and wipe (or create) for reading and writing. a+ // Open a file for reading and appending. Offset values: SEEK_SET // Start of file. SEEK_CUR // Current location. SEEK_END // End of file. Math library -- #include <math.h>: double sin( double x ) // Sine of x (in radians). double cos( double x ) // Cosine of x. double tan( double x ) // Tangent of x. double asin( double x ) // Inverse sine of x. double acos( double x ) // Inverse cosine of x. double atan( double x ) // Inverse tangent of x. double sinh( double x ) // Hyperbolic sine of x. double cosh( double x ) // Hyperbolic cosine of x. double tanh( double x ) // Hyperbolic tangent of x. double exp( double x ) // Exponential function -- e^x. double log( double x ) // Natural log of x. double log10( double x ) // Base 10 log of x. double pow( double x, double y ) // Power function -- x^y. double sqrt( double x ) // Square root of x. double ceil( double x ) // Integer >= x (returned as double). double floor( double x ) // Integer <= x (returned as double). double fabs( x ) // Absolute value of x. Standard utility library -- #include <stdlib.h>: double atof( char *nvalstr ) != 0 // Convert numeric string to double. int atoi( char *nvalstr ) != 0 // Convert numeric string to int. long atol( char *nvlastr ) != 0 // Convert numeric string to long. int rand() // Generates pseudorandom integer. srand( unsigned seed ) // Seed random-number generator. exit( int status ) // Exits program. int system( char *syscmd ) == 0 // Execute system program. int abs( int n ) // Absolute value of int. long labs( long n ) // Absolute value of long. Time & date library -- #include <time.h>: time_t time( time_t *timeptr ) // Current time count as long int. char *ctime( time_t *timeptr ) // Current time & date string. String function library -- #include <string.h>: int strlen( char *s ) // Length. strcpy( char *dst, char *src ) // Copy. strncpy( char *dst, char *src, size_t n ) // Copy n characters max. strcat( char *dst, char *s ) // Concatenate. strncat( char *d, char *s, size_t n ) // Concatenate n characters. strcmp( char *s1, char *s2 ) == 0 // Compare. strncmp( char *s1, char *s2, size_t n ) == 0 // Compare n characters. stricmp( char *s1, char *s2 ) == 0 // Compare, no case. strnicmp( char *s1, char *s2, size_t n ) == 0 // Compare, no case, n chars. char *strchr( char *s, int ch ) != NULL // Find first character. char *strrchr( char *s, int ch ) != NULL // Find last character. char *strstr( char *dst, char *src) != NULL // Find string. char *strlwr( char *s ) // Lowercase. char *strupr( char *s ) // Uppercase. Character class test library -- #include <ctype.h>: int isalnum( int c ) != 0 // Alpha / digit. int isalpha( int c ) != 0 // Alpha. int iscntrl( int c ) != 0 // Control character. int isdigit( int c ) != 0 // Decimal digit. int isgraph( int c ) != 0 // Printing character (except space). int islower( int c ) != 0 // Lower-case. int isprint( int c ) != 0 // Printing character (including space). int ispunct( int c ) != 0 // Printing character but not space/alnum. int isspace( int c ) != 0 // Space, FF, LF, CR, HT, VT. int isupper( int c ) != 0 // Upper-case. int isxdigit( int c ) != 0 // Hex digit. int tolower( int c ) // Convert to lower case. int toupper( int c ) // Convert to upper case. Dynamic memory allocation -- #include <malloc.h>: buf = (<type> *)malloc( (size_t)sizeof( <type> ) <array size>) != NULL free( <type> *buf )