1. Introduction to C
CSCE 343

2. Hello World

3. Comments Multi-line comments only in standard
/* … */
Single line comments allowed in certain compilers:
// …

4. Declarations
In C standard, all declarations must appear above regular code.
char red;
int j;
for (int i =0; i < 10 : i++){ }
Not required in newer compilers.

5. Compiling using Cygwin gcc
The gcc compiler (GNU Compiler Collection) is on the lab machines through cygwin.
gcc –o hello hello.c
./hello
On shemp, same process.

6. Cygwin UNIX environment on Windows
Provides many of the UNIX/Linux utilities
Differences from regular DOS prompt:
Uses forward slash for directory separator
Uses ls not dir
Must be run from Cygwin icon
Available for free download.

7. main Similar to public static void main
Return value indicates success/failure to shell.
0: success
Non-zero: failure

8. Arrays No new operator in C: Brackets do not follow type
int a[10]; // array of ints
char *b[20]; // array of pointers
// to char
Brackets do not follow type
Except in prototypes
No array index bounds checking!
No length variable
sizeof(a) / sizeof(a[0])

9. Pointers Dereferencing operator: * Address operator: &
Except in declaration
Address operator: &
Declaring pointers:
int * xPtr; // Pointer to int
char * cPtr; // Pointer to char
int y,x =5;
xPtr = &x; y = *xPtr + x;
Act very much like references in Java, but not quite the same.
Can point to primitive types
Can do arithmetic on pointers

10. Arrays and Pointers
Array name (without brackets) is an alias to a pointer to the first element in the array.
Arrays can be traversed with pointers.
Brackets can be used with pointers.
int a[10];
int *aPtr;
aPtr = a;
aPtr[6] // same as a[6]
*(aPtr + 6) // same as aPtr[6]

11. Strings Arrays of char Terminated with the null character: ‘\0’
Array can be longer than the string
Must be longer by at least one.
Can’t concatenate with +
Use strncat
strcat(st1,”def”); // st1+”def”

12. Types Usual suspects: Unusual: No boolean data type Examples
int, char, double, float, short, long ...
Unusual:
long long, unsigned int, …
No boolean data type
0 false
Non-zero true
Any numeric or pointer type works!
Examples
if (0)
if (y=0)
if (y==0)

13. Input stdin: alias for the console
standard input
Two main choices for reading from stdin:
scanf: input formatted data directly into variables
reading strings the \n is left in the input stream
fgets: read a full string, including \n, parse it yourself, \n is part of the resulting string
String to int: atoi
String to float (double): atof

14. Struct Encapsulation construct Encapsulates data, but not methods
Everything is public (no access restriction)
No inheritance
struct employee{
int id;
char name[NAME_LEN+1];
double salary;
} emp1,emp2;
struct employee emp3;

15. typedef Define new types
Commonly used to define a type name for struct
typedef struct{
int id;
char name[NAME_LEN+1];
double salary;
} Employee;
Employee emp1,emp2;

16. File I/O <stdio.h>
Basic file access tool: file pointers
FILE *filePtr;
Open/close: fopen, fclose
filePtr = fopen(“fileName”, “r/w/a/r+w/…”)
fclose(filePtr)
Reading:
fgets (stg, 100, filePtr) //line at a time: check for NULL
getc(filePtr) //char at a time: check for EOF
Writing
fprintf (filePtr, stg)
fprintf(filePtr, “format string”, variable-list)