Working with the Unix OS

C Programming – Basics
| expr3;
| }
exprl, expr2 and expr3 may be as complicated as you like
do
statement
while (expression)
This is a post-tested loop which continues to execute while expression is non-zero.
! Multi-way Decision
switch (expression)
{
case optionl : statement list
case option2 : statement list
...
case optionN : statement list
default: statement list
}
Notes:
- similar to 'case' in Pascal
- execution starts at the statement list which has a label corresponding to the value of the expression and
continues through all remaining statement lists
To stop processing in the middle of a switch statement, a break statement can be used to terminate execution of
the current block.
Functions Returning Non-integers
Often functions return (void) or int
Many functions like sqrt, sin, and cos return double
#include
double atof(char s[]) /* atof: convert string s to double */
{
double val, power;
int i, sign;
for (i=0; isspace(s[i]); i++); /* skip white space */
sign = (s[i] == '-') ? -1 : 1;
if (s[i] == '+' || s[i] == '-') i++;
for (val=0.0; isdigit(s[i]); i++)
val = 10.0*val + (s[i] - '0');
if (s[i] == '.') i++;
for (power=1.0; isdigit(s[i]); i++) {
val = 10.0*val + (s[i] - '0');
power *= 10.0;
}
return sign*val/power;
}
The calling routine must know what atof returns thus all functions should be explicitly declared.
#include
#define MAXLlNE 100
main() /* simple calculator */
{
double sum, atof(char []);
char line[MAXLlNE];
int getline{char line[], int max);
sum = 0;
while (getline{line, MAXLlNE) > 0)
printf{"\t%g\n", sum += atof(line));
return 0;
}
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