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("%s", 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");

16.	            
int **array;
int i,j,10;
array = malloc(10*sizeof(int *));
for(i=0;i<10;i++)
for(j=0;j<10;j++)
array[i][j] = i*j;

17.	       
int x=5;
if (x=1)
printf("one.\n");
else
print("not one.\n");

18.	    
int x,y;
char s[50];
scanf("%d %d %5s",x, y, s);

19.	
int main(int argc, char *argv[]) {
printf(argv[1]);
}

20.	
int main (a) { 
if (a > 5)
return(1); 
}

21.	    
int i;
...
while(i>0);
printf("i=%d\n",i--);

22.	
char *get_result () {
   char result[80];
   sprintf(result, 
"here is the result.");
   return(result);
}

int main() {
   char *p;
   p = f();
   printf("f() returns: %s\n", p);
}

23.	    
char s[50];
scanf("%50s",s);
s[50] = '\0';

24.	    
int i,x[10];
for(i=0;i<=10;i++)
x[i]=i*2;

25.	  
int *array;
int i,j;
for(i=0;i<5;i++) {
array = malloc(5*sizeof(int));
for(j=0;j<5;j++)
array[j] = i*j;
}

26.	 
int* x,y;
 ...
printf("%d\n",*y);

27.	
char *str,*p;
...
p=str;
while(*p!=0) {
*p++;
p++;
}

28.	
int a, b;
char buf[100];
scanf("%d %d", &a, &b);
sprintf(buf, "result: %d %d");

29.	    
int getval(char* mystring) {
char *p, *malloc();
p = malloc(25);
scanf("%s", p);
mystring = p;
free(p);
}

30.	    
#define cube(x) 	x*x*x
#define double(x) x+x
x = 3;
y = cube(x + 1);
z = 5 * double(x);

31.	        
char *str;
int x;
...
switch(str) {
case "one": x=1; break;
case "two": x=2; break;
case "three: x=3; break;
default: x=0;
}

32.	  
int i;
...
switch(i) {
case 1: printf("One.\n");
case 2: printf("Two.\n");
case 3: printf("Three.\n");
default:printf("Something
Else.\n");
}

33.	    
char c = "a";

34.	
#define mytan(x) 	sin(x)/cos(x)
x = 3;
y = myfunction(x++);

35.	    
if (x < 0) {
printf("Invalid value.\n");
exit;
}