Description

C Basic
Jason Zixu Zhou
Slides are revised from Murray Kornelsen

Integer Types
Type Size Range
char unsigned char 1 byte (8 bits) -128 to 127
0 to 255
short unsigned short 2 bytes -32768 to 32767
0 to 65535
int
unsigned int 4 bytes -231 to 231-1
0to 232-1
long unsigned long 8 bytes -263 to 263-1
0to 264-1
• Note that types can differ between compilers.
– Example: MSVC defines long as 4 bytes and “long long” as 8 bytes.
• This table applies for 64-bit gcc.
Float Types
Type Size
float 4 bytes
double 8 bytes

• More complex type which stores numbers as a sign, exponent, and fraction.
• Probably not needed for this course.
Variables
• Syntax
– <data type> <name>;
• Value undefined.
– <data type> <name> = <value>;

Separate C Files
• To organize your code, you may want to put functions in different files.
• To call a function in a different file, you need a forward declaration.
– Just tells the compiler “this function exists somewhere”.
– Compiler works top to bottom.
File1.c File2.c

Header Files
• Placing forward declarations in every C file will not scale well.
• Header files hold function declarations (and more), for convenient use with #include.
Funcs.h Funcs.c Main.c

Types of .h files
• System headers
– #include <stdio.h>
– #include <stdlib.h>
– #include <string.h>
• User made headers
– #include “Funcs.h”
• <…> used when including system headers.
• “…” searches local directories first and should be used with your headers.

Pointers
• A pointer is just a 64-bit unsigned integer that represents a memory address.
• Can store the address of a large block of memory (malloc).
• You can define pointers for any type.
– Including pointers to pointers.
– Another C lab will go in depth later.
– “*” is used to declare and dereference pointers. – “&” is used to get the address of a variable.
• Syntax:
– <datatype> * <name> = &<variable>

Arrays and Pointers
• In C, pointers and arrays are interchangeable in many ways.
– One important difference:
• sizeof(ptr) = 8
• sizeof(array) = sizeof(dtype) * length
– When you pass an array to a function, it will be handled as a pointer.
• You can index a pointer in the same way as an array using [ <idx> ].
String Creation
• C strings are just arrays of char terminated with the null character ‘’.
• Initialization
– Array: char str[] = “Hello”;
– Pointer: char *str = “Hello”;
– Specified size array: char str[100] = “Hello”;
• Important: if you use the pointer method, you cannot modify any characters in the string.
– This creates a pointer into read-only memory.
– Can use malloc or strdup to get a modifiable string.
String Functions
• The standard library contains various useful string functions.
• #include <string.h>
Function Description
int strlen(char *str) Returns the length of a string.
int strcmp(char *a, char *b) Returns 0 if strings are identical. Otherwise returns some “difference”.
char *strcat(char *dst, char *src) Appends string src to dst.
char *strcpy(char *dst, char *src) Copy src into dst buffer.
char *strdup(char *src) Allocates memory and copies src to it. Need to free the returned pointer.

Structs
• Structs can be used to create groups of data.
– Simpler than “objects”.
• Values can then be accessed by name.

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