CS 241: System Programming Fall 2008
C No Evil Homework Due start of class, Friday, September 5, 2008
Each of these examples can appear inside C programs. The ... means additional (irrelevant) instructions.
For each example, answer the following questions:
(a) What does the code attempt to do?
(b) Why does it not work correctly?
(c) How can the code be corrected?
1.
int x, *ip;
float y, *fp;
...
ip = &x;
fp = (float *)ip;
y = *fp;
2.
int x,*p;
*p=x;
3.
int **array = (int **)
malloc(n*sizeof(int));
4.
int x;
scanf("%f",&x);
5.
void increment(int x) {
x++;
}
...
for(x=0;x<10;increment(x)) {
printf("x=%d\n",x);
}
6.
char str[5];
strncpy("abcde",str,5);
printf(โ%sโ, str);
7.
int *p;
p = 0;
*p = 12;
8.
void test(char*s1, char*s2) {
return strcmp(s1,s2) == 0;
}
9.
int *p;
int *q;
p = q;
*p = 30;
10.
char *s;
s=(char *) malloc (100);
s="hello";
free(s);
11.
char somespace[8];
strcat(somepace,"12345678");
12.
int *array;
int i,n;
...
for(i=0;i<n;i++)
array[i] = i*i;
13.
char s1[5] = "word";
char s2[5] = "word";
if (s1 == s2)
printf("The strings are equal.\n");
14.
int a;
if (0 < a < 5)
printf("a is greater than 0 but less
than 5.\n");
15.
int a,b;
if (a =! b)
printf("a and b are not the
same.\n");
