LEC 2 Flashcards
*
– evaluate expression to integer
– use integer as address to get value from memory
*(&name)
get address associated with name
get value from memory at that address
assignments are
expressions
space allocated to declarations on ?
on stack
while(expression
while(expression)
statement ->
- evaluate expression
- if non‐zero then
i. execute statement
ii. repeat from 1. - if zero then end iteration
• break in statement ends enclosing iteration
Iteration: for
for(exp1;exp2;exp3)
statement ->
exp1;
while(exp2)
{ statement
exp3;
}
- execute statement exp1
- repeatedly test exp2
- each time exp2 is true
- execute statement
- execute statement exp3
• all exps and statement
are optional
Condition: if
if(expression)
statement1
else
statement2 ->
- evaluate expression
- if non‐zero then execute statement1
- if zero then execute statement2
• else statement2 is optional
Condition: switch
switch(expression)
{ case constant1: statements1
case constant2: statements2
...
default: statementsN
}
- evaluate expression to a value
- for first constanti with same value, execute statementsi
- if no constants match expression, evaluate default
statementsN
Function declaration
type name(type1 name1,...,typeN nameN)
{ declarations
statements
}
- evaluate expression to a value
- for first constanti with same value, execute statements
- if no constants match expression, evaluate default
statementsN
Function call
name(exp1,…,expN)
- evaluate expifrom left to right
- push expi values onto stack
- execute body, allocating stack space to any
declarations - reclaim stack space for parameters & any
declarations - return result if any
• NB end statement function call with ;
Changing parameters
• parameters passed by value
• value of actual parameter copied to space for
formal parameter
• final value is not copied back from formal to
actual
• so changing the formal does not change the
actual
Pointers
type*name;
• variable name holds address for byte sequence for type • allocates stack space for address but does not create instance of type • must allocate space explicitly NULL • empty pointer
How to actually change parameters?
• to change actual parameter
– pass address (&) of actual to formal
– change indirect (*) on formal
What is FILE?
• type for system representation of file
• all files are treated as text
– i.e. character sequences
FILE * name;
• name is the address of a FILE value
FILE * fopen(path,mode)
• open file with path string
• return
– FILE address
– NULL if no file
• mode
– “r” – read
– “w” – write – create new empty file – delete old version!
– “a” – append i.e. write at end of existing file
fclose(FILE *)
- close file
- system may not do this for you when program stops
- for I/O, C handles characters as ints
- EOF == system end of file constant
int getc(FILE *)
• return next byte from file address
– as int
• return EOF if at end of file
int putc(int,FILE *)
• puts int to file address
– as byte
• return EOF if failure
main(int argc; char ** argv)
• argc == number of command line arguments
– including call to executable
• argv == pointer to pointer to char – i.e. pointer to sequence of char • i.e. array of strings – argv[0] == name of executable – argv[1] == 1st argument – argv[2] == 2nd argument
exit(int)
end program
• return value of int to outer system
• in stdlib library
file copy
$ copy path1 path
- check correct number of arguments
- open file1
– check file1 exists - open file2
– check file2 exists - copy characters from file1 to file2 until EOF
- close files
formatted input
int fscanf(FILE *,”format”,exp1,exp2...) – expi == lvalue
formatted output
int fprintf(FILE *,”format”,exp1,exp2...) – expi == rvalue
