C Lecture 2

Functions

return-type
function-name ( arg-1-type arg-1-name ,
	        arg-2-type arg-2-name , etc )
{
    function-body
}

    int
    strlen(char *str)
    {
        int len;

	for (len = 0; str[len]; len++)
	    ;
	return len;
    }

    double
    poweri(double val, int power)
    {
	int sign = 1;
	int i;
	double result = 1.0;

	if (power < 0) {
	    sign = -1;
	    power = -power;
	}
	for (i = 0; i < power; i++)
	    result *= val;
	if (sign < 0)
	    result = 1 / result;
	return result;
    }

#include <stdio.h>

char *
fgets(char *buf, int bsize, FILE *fp)
{
    int i;
    int c;
    int done = 0;

    if (buf == 0 || bsize <= 0 || fp == 0)
        return 0;

    for (i = 0; !done && i < bsize - 1; i++) {
        c = fgetc(fp);
        if (c == EOF) {
            done = 1;
            i--;
        } else {
            buf[i] = c;
            if (c == '\n')
                done = 1;
        }
    }
    buf[i] = '\0';

    if (i == 0)
        return 0;
    else
        return buf;
}

Memory Layout (simplified)

• instruction (aka text)
  • contains program itself (instructions for the CPU)
  • typically read only
• data
  • contains global variables
  • read/write
• stack
  • contains function parameters, local variables and `function call stack'
  • read/write