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  Value and type of last evaluated expression: Address of array element: Address of array elementx:  (none)

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Code

 Header...
#define NDIM 2 typedef struct particle { float x[NDIM]; float mass; struct particle *next; }Particle; // Allocate a new particle and add it to the start of the list
struct particle* newparticle(Particle *first){
  ...
» Particle *p; » p=xmalloc(sizeof *p); » p->next=first; // Now initialise exactly as before » printf("Please enter the mass and x and y values.\n"); » scanf("%f %f %f", &p->mass, &p->x[0], &p->x[1]); » return p;
} // !! This function demonstrates a memory leak /* * Free Particle "togo" and return the new first Particle * "first" must be the existing first member of the list */ struct particle* freeparticle(Particle *togo,Particle *first){
  ...
» Particle *parent; » if (togo==NULL) // Do nothing return first; else if (first==NULL) { » fprintf(stderr, "Trying to remove something from an empty list!\n"); » return NULL; } » if (togo==first) // Is it the first one? first=first->next; else {// Find togo's predecessor: » for (parent=first; parent->next!=togo; parent=parent->next) { » if (parent->next==NULL) { » fprintf(stderr, "%p isn't in the list!\n", togo); » return first; } } » parent->next=togo->next; } // free(togo); » return first;
} int main(){
  ...
» int i, n; » Particle *first=NULL; » printf("How many structures would you like?\n"); » scanf("%d", &n); » for (i=0; i<n; ++i) first=newparticle(first); // Demonstrate some cases of freeing a particle » Particle *killme=first->next->next; » first=freeparticle(killme, first); » killme=first; » first=freeparticle(killme, first); » killme=NULL; » first=freeparticle(killme, first); » for ( Particle *p=first;p!=NULL; p=p->next) printf("Mass: %f position: (%g, %g)\n", p->mass, p->x[0], p->x[1]); » return 0;
}
Memory

Allocated memory

128
129
130
131
132
133
134
135
128.x[0] = 2.30507e+13
128.x[1] = 4.00822e+25
136
137
138
139
140
141
142
143
128.mass = -1.57003317e-13
128.next = -133234636

152
153
154
155
156
157
158
159
152.x[0] = -5.14246e-27
152.x[1] = -3.79733e+37
160
161
162
163
164
165
166
167
152.mass = -28994412
152.next = -131928658

176
177
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180
181
182
183
176.x[0] = 1.57105e+33
176.x[1] = 5.26257
184
185
186
187
188
189
190
191
176.mass = -5.03155023e+31
176.next = -129269290

200
201
202
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204
205
206
207
200.x[0] = -9.94627e+20
200.x[1] = 1.06335e-29
208
209
210
211
212
213
214
215
200.mass = -3.23415139e-21
200.next = -129956580

freeparticle()

344
345
346
347
348
349
350
351
first = -4153472432
togo = -4153472432
360
361
362
363
parent = 504

freeparticle()

344
345
346
347
348
349
350
351
first = -4153472456
togo = NULL
360
361
362
363
parent = 504

freeparticle()

344
345
346
347
348
349
350
351
first = -4153472432
togo = -4153472480
360
361
362
363
parent = 504

newparticle()

348
349
350
351
first = -4153472480
360
361
362
363
p = 504

newparticle()

348
349
350
351
first = NULL
360
361
362
363
p = 504

newparticle()

348
349
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351
first = -4153472504
360
361
362
363
p = 504

newparticle()

348
349
350
351
first = -4153472456
360
361
362
363
p = 504

main()

456
457
458
459
460
461
462
463
i = 1
n = 200
464
465
466
467
468
469
470
471
first = NULL
killme = -4153472480

main(): for()

472
473
474
475
p = -4153472456

NB: the actual memory address of each variable is the
address shown plus 4294428896 (0xFFF7C8E0).

The actual address of allocated memory is the
address shown plus 140956264 (0x866D268).

Show Advanced options

.

Input was:

4 
4.1 2.4 7.7 
5.0 6.3 8.6 
3.6 4.3 2.91 
7.2 5.7 6.1

Show output (Before looking at the output, work out what you think it put should be and see if you are right.)

Output

How many structures would you like?
Please enter the mass and x and y values.
Please enter the mass and x and y values.
Please enter the mass and x and y values.
Please enter the mass and x and y values.
Mass: 3.600000 position: (4.3, 2.91)
Mass: 4.100000 position: (2.4, 7.7)
                                                                                                                                                                                                                                                                       

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