Working with the Unix OS

C Programming – Basics
e.g.
i += 2 adds 2 to i
7. Increment - Decrement Operators {++, --}
a++ is equivalent to a = a+l
++a is equivalent to a = a+l
b = a++ is equivalent to b = a; a = a+l;
b = ++a is equivalent to a = a+l; b = a;
Functions
A function in C is very similar to a function in FORTRAN.
e.g.: a max function
int max(a,b)
/* A function to compute the maximum of two
integers */
int a,b ;
{
if a > b
return(a) ;
else
return(b) ;
}
Notes:
- the type of the function appears first.
- there is no semicolon between the function header and the formal
- parameter declarations.
- results are passed back using the return statement.
- all parameter passing is call by value.
The default type for a function is int and so can be omitted in this case. Even if a function has no parameters its
name must be followed by parentheses,
e.g.
void say_hello()
{
printf ("Hello World\n");
}
Control Structures
! Binary Decision
if (expression)
statement1
else
statement2
Notes:
- the expression must be enclosed in parentheses
- the expression is considered false if it evaluates to 0 and true, otherwise
- as in Pascal, elses associate with the nearest ifs
- as the semicolon is a terminator in C they will occur before elses
! General Loops
while (expression) statement: provides a pretested loop.
C also provides a for statement which is a useful shorthand for an often occurring while statement form.
These two constructs are equivalent
for (exprl;expr2;expr3) | exprl;
statement;
| while (expr2)
| {
| statement
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