how to sum 500 numbers

[john27]

Hello all,

Could anyone please help me writing a code to sum a 500 numbers from 2-arrays.

heres what i wrote so far

unsigned int a[500];
unsigned int b[500];
int i;
unsigned int answer;
 
   for ( i=0; i<=1000 ; i++)
{ answer= a[i]*b[i];

.......
}

what shall i do next to get the sum of all the values ?

thank you

[quzah]

How do you store a value?
How do you add to that value?

Answer those two questions, and you will have your answer.


Quzah.

[john27]

thanks quzah ... yeah the problem is i am not sure hot to add to that value .. so i am a newbie to programming

[tabstop]

Well, you know how to multiply, as we see that in the code. Surely you know what symbol is used for addition? (Hint: It's '+'.)

[john27]

haha
well, thank you
is something like that correct ?

unsigned int a[500];
unsigned int b[500];
int i;
unsigned int answer[];
unsigned int sum=0; 
   for ( i=0; i<=1000 ; i++)
{ answer[i]= a[i]*b[i];
sum= sum+answer[i];
}

thanks

[tabstop]

You need to give a size for the answer array. Your loop goes to 1000 but you only have 500 pairs of numbers.

[anduril462]

Yes, something like that, but definitely not that:

unsigned int a[500];
unsigned int b[500];
int i;
unsigned int answer[];
unsigned int sum=0; 
   for ( i=0; i<=1000 ; i++)
{ answer[i]= a[i]*b[i];
sum= sum+answer[i];
}

Egad! Where are those other 500 numbers coming from? a and b are only defined for indexes 0 to 499, but your loop tries to index all the way through 999. Also, you should probably give answer a size. I reckon 500 would be good there too, once you change your loop. This sounds like a perfect opportunity to put in a plug for named constants (i.e. not bad juju magic numbers like 500 and 1000) and indentation:

#define SIZE 500  // hooray for constants...want to change the size?  only one place to change it instead of 4
unsigned int a[SIZE];
unsigned int b[SIZE];
int i;
unsigned int answer[SIZE];
unsigned int sum = 0;

for (i = 0; i < SIZE; i++) {
    answer[i] = a[i] * b[i];
    sum += answer[i];  // that's shorthand for sum = sum + answer[i]
}

[john27]

 
unsigned int a[500];
unsigned int b[500];
int i;
unsigned int answer[2];
unsigned int sum=0; 
   for ( i=0; i<=500 ; i++)
{ answer[i]= a[i]*b[i];
sum= sum+answer[i];
}

?

[john27]

thank you guys

[tabstop]

If you think that 2 is the same number as 500, this is going to be a long thread.

[quzah]

This thread teaches us: You can do a man's work for him, but you can't teach a man to think.


Quzah.

[anduril462]

unsigned int answer[2];

Why would you only make answer an array of 2 ints? Your loop runs i from 0 to 500 (should be 499, see below), and tries to access answer[i], which will be invalid for any values of i other than 0 or 1.

for ( i=0; i<=500 ; i++)

Drop that = sign. Your array has 500 elements, but the valid indexes are 0..499 (it's always 0..size-1 in C). Your loop goes one too far, and tries to access a[500] and b[500], which don't exist.

I think you just missed my post when you were replying, it gives a good solution to all your array size and loop troubles. Scroll up a little...

[john27]

thank you anduril462 ... I appreciate your help ... and for the others , bravo