Seemingly simple array program yielding bizarre output

Quote:

---

#include <stdio.h>
#include <stdlib.h>


int main(void) {
int grades[10];
int i, sum;

for (i=0; i<=10; ++i)
{
sum = sum+grades [i];

printf("\n %d",sum);

}
return 0;
}

---

Output:

Quote:

---

2009291924
2009147472
-1
2009288233
2009288258
4200880
2359128
4200982
4200880
2354536
10

---

Tried my best to debug & finally gave up. IMO output is irrelevant. Kindly help.

Both sum and grades are uninitialized, meaning they will contain what ever garbage happens to reside at that memory location currently.

To initialize them:

Code:

---

int grades[10] = {0};
int i, sum = 0;

---

That way they will have initial values of 0. Another thing I noticed is that your loop gives you 11 outputs, (meaning you print one value outside the array) due to the condition: i <= 10
you probably want: i < 10

This comes down to how arrays are indexed, starting from 0, so in your case valid indexes are 0-9.

Thanks! that helped a bit & I have tweaked the program a little. Why isn't value of sum changing when i is getting iterated? I am sorry if my doubts are slightly noobish; I am just working on some basic concepts of C programming.

Code:

---

#include <stdio.h>
#include <stdlib.h>


int main(void) {
int grades[5] = {0};
int i, sum = 0;

for (i=0; i<5; ++i)
{
        sum = sum+grades [i];

printf("\n%d \t%d",i, sum);
}

return 0;
}

---

Output:

Code:

---

0    0
1    0
2    0
3    0
4    0

---

Quote:

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Originally Posted by alter.ego

Why isn't value of sum changing when i is getting iterated?

Code:

---

...
int grades[5] = {0};
...
for (i=0; i<5; ++i)
{
        sum = sum+grades [i];
}
...

---

---

The statement "grades[5] = {0}" will set all the members of grades to 0, meaning that each time through your loop you're adding 0 to sum, so it stays the same.

Yes, there are no grades in your array. If you want to sum grades, you must first input these grades into the array, how else can you sum them?

Edit: you can initialize the array with the grades if you want to.

Code:

---

int grades[5] = {1, 2, 3, 4, 5};

---

That's a great enlightment for me (if I understood correctly).

So for loop just references the memory location where the values are initialized. It doesn't actually provide the values in int grades[5]. Am I in right direction?

Yes, if you are talking about your specific for loop here, you are stepping through the array with the index and adding them one at a time to sum.

Thanks guys! Got it. Much appreciated.