C has basic data types, variable scoping etc
it does not deal with composite objects such as strings, sets, lists, arrays etc no heap, no gc
c offers only single threaded control flow c is a small language, it can be learned quickly. use it to the maximum to get its real benefits
ansi-c was the new defination for the language that was set as the standard after the recommendations of the ansi committe it introduced a library to go with c
since the data types and the control structures provided and used by C are supported directly by most computers, the run time library for c is small
c is not a strongly typed language its type-checking has strengthened
c has a standard library after the ansi committe which has io functionality the ansi standard defines the official syntax and semantics of c
hello world!
#include <stdio.h> main() { printf(“hello, world\n”); }
compile using gcc -o hello hello.c
the c program consists only of 2 things - functions and variables it doesnt have classes, metaclasses etc
we used a function called main in the above example the execution starts from main() function (like in Java) note, we imported the standard input output library we communicing data between functions via arguments printf is a library function
#includef <stdio.h>
main() { int fahr, celsius; int lower;
lower = 0; while (fahr<=upper) { e = 5*(fahr*32)/9; printf(“%d\t%d\n”, fahr, celsius); fahr=fahr+step; } }
comments are: /*
*/
in c, all variables must be declared before they are used we have these datatypes: char,short, long, double, char is a single byte
single statement without braces, or braces for multiple statements integer division trucates, the fractional part is removed the first arguemnt for printf is a string and the succeding arguments are replacements for the %s in the string
printf is not a part of C itself. there is no output or input defined in C itself
%6.1f means that 6 characters before the decimal, 1 after it %.2f means 2 after the decimal, unlimited before it
%d is for integers %f is for floats %o octal %x hexadecimal %c character %s string %% to print %
the for statement is like java as well
int i; for (i=0; i<100; i++) printf(“as”);
a general rule - in any context where it is permissible to use the value of a variable of some type, you can use a simpler form of that variable
magic numbers are numbers that control the terminating conditions etc in the script we should define them early in the script eg: #define LOWER 0 note, no semicolon when they end
we can print one char at a time using putchar getchar reads the enxt char and returns it as its value
program to write back what is read: #include <stdio.h>
main() { char c = getchar() while (c!= EOF){ putchar(c); c = getchar(); } }
what looks like a character on the screen is stored inside as a bit pattern (which is decided based on the encoding followed)
when there is no more data to get, getchar returns EOF, a special value if we had used char to store the characters above, it wouldnt have been able to store EOF EOF is an integer defined in stdio.h
EOF has value of -1
to print long integer, use %ld %f is for float and double %0.f prints only the integer part of the float
for(nc=0;getchar()!=EOF, ++nc) ; //this is a null statement, for the for loop body
if (c==’\n’) ++n1;
you can do: printf(‘%i’, ‘A’); to get 65 printed (ascii coding) \n is 10 in ascii, it is a single character
note we could do that because we use single quotes, if we use double quotes, it wont be done, it will be treated as a char
wc is a word count utility of unix, it is just an elaborate c program that counts the words it is written in c, maybe? yes, most probably
c has arrays int ndigit[10]; just like in java zero indexed they are
with properly designed functions, it is possible to ignore how a job is done, knowing what is done is sufficient
write a function this way:
int power(int base, int n): { int i, p; p = 1; for (i=1; i<=n; i++) p = p*base; return p; }
int is the return type, power is the funciton name
parameter - variable named in the paraenthesized list in a function definaton above, base and n were paramenters
argument - value used in a call of the function eg: power(a, b), a and b are arguments
we can have an empty return statement which returns the control to the calling funciton, without any value the main function too must return values to the enviornment that calls it - 0 for normal termination, other values for other things
we must also declare the function in the main to be able to use it, by providing the function prototype eg: int power(int, int); or better, give argument names as well, int power(int base, int exponent);
in C, arguments are passed “by value” and not by reference as in java. recall python also has pass by reference, but some datatypes like strings are immutable so, they become pass by value effectively
we can still pass by reference if we pass the pointer to the varialbe
when we pass an array as an argument, the address of the beginning of the array is passed.
#include <stdio.h>
#define MAXLINE 1000
int getLine(char Line[], int maxline); void copy(char to[], char from[]);
main() { int len; int max; char line[MAXLINE]; char longest[MAXLINE];
max=0; while((len=getline(line, MAXLINE))>0) if (len>max){ max=len; copy(longest, line); } if (max>0) printf(“%s”, longest); return 0; }
Now creating the functions getline and copy int getline(char s[], int lim) { int c, i; for (i=0;i<lim-1 && (c=getchar())!=EOF && c!=’\n’; ++i) s[i]=c; if (c==’\n’) { s[i]=c; ++1; } s[i]=’\0’; return i; }
void copy(char[] to, char[] from){ int a=0; while((to[i]=from[i])!=’\0’) ++i; }
\0 is the null character, its value is 0 used to denote the end of something - eg, strings etc
reverse a string in c: #include <stdio.h> #define MAXLINE 1000
main() { char line[MAXLINE] int i=0; char c; for (i=0; (c=getchar())!=EOF; i++){ line[i] = c; } while(i>0){ putchar(line[i]); –i; } }
variables that are defined in a function have their scope limited to that function they life is limited to the life of the function creating them, so they are called “variables local to that function” or automatic variables
you can have external variables as well. if you define them outside the main, they can be called by any function
function prototype of a function that doesn’t take any arguments and return anything void fn_name(void)
if you want to use the external variable in any function, you have to mention it using extern int variableName; however, you dont have to do this if you place the variable before the function defination hence, common pratice - define all the external functions before any function defination
if the code is split across several files, collect all the external variables and functions in a file called header and include it in each source file using #include the suffix .h is conventional for header names eg: the functions of the standard library are declared in stdio.h header file
defination of a variable - when the variable is created or assigned storage declaration of a varialbe - variable type is stated, but no storage is assigned
c comments do not nest
there are two types of integer types - signed and unsigned we have long double type for extra precision enumerations are part of the language we can define objects as const which prevents anyone from changing them
the basic datatypes in C: char - a single byte, for holding one character 1 byte - 8 bits - 256 possibilities, so any character included int - an integer float - a float double
short and long apply to integers
short is 16 bits, long is 32 bits int is either 16 or 32 we also have signed or unsigned ints signed means the varialbe has sign, can be negative unsigned means only 0 and positive
so, in 1 byte, unsigned can be 0 t0 256 and signed can be -128 - 127
the header files limits.h and float.h contain symbolic constants for all these sizes
l is long ul is unsigned long similarty f and uf
integer can also be defined in octal and hexadecimal leading zero means octa leading 0x means hexadecimal so, 31 can be written as 037 in octal and 0x1f or 0x1F in hex to make them long or unsigned, follow them by L or U respectively
also, characters in a single quotation means we are referring to their ascii codes so, 48 == ‘o’ also, ‘\n’ is one character only
we can also represent an arbitary byte sized bit pattern is: \ooo where ooo is one to three digits of octal or, \xhh where hh are 2 hexadecimals. so:
#define VTAB ‘\013’ // ascii code 3*1+1*8+0*64 - 11 is same as: #define VTAB ‘\xb’ //b in hex is 11