What does "sum += many[i]" do?

Hi there,

That takes the value of sum and adds the value of many[i] to it, and assigns that back into the value of sum.

I assume that iterates through the array many[] using an index of i so that you end up with sum having the value of all the elements of many[] added up.

Hope that helps!

Steve.

sum += many[i]

In this case, many is an array. You can tell because it has the square brackets []. The variable i is a way to access one of the indexes of that array.

So, sum += many[i] is saying, take what is currently in sum, and add whatever is inside many at index i.

It could also be written as sum = sum + many[i].

I is often used as a looping variable for a for loop. So, with this sum += code snippet inside a loop and the index starting at zero, and running until the size of the array, you would be able to sum up all the integers in the array.

Hi,

I had to watch the video several times, and go through many of the Q&As to finally understand it. I broke it down the loops into steps according to my understanding, hopefully this helps.

int many [] = {2, 4, 8};

int sum = 0;

for (int i=0; i (< 3); i++)

{sum += many [i];

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

         //Remember, *when:  
         0 refers to 2,  
         1 refers to 4,   
         2 refers to 8

——————————————————————————————————

Loop 1:

1a. i=0

1b. i (0) < 3

         // 0 is less than 3, loop continues.

1c. sum += many[i]

         // translation, everything in parenthesis. 

         many [i], pulls input from step 1a. 

          = sum (0) += many[i (*when: 0)]  = new_sum_A = 2  

1d. printf("sum %d\n", sum)

          // “sum (new_sum_A)”  = Output A: sum 2

1e. i++ = (i=0) + 1 = 1

         // i=1

——————————————————————————————————

Loop 2:

2a. i=1

2b. i (1) < 3

         // 1 is less than 3, loop continues.

2c. sum += many[i]

         // translation, everything in parenthesis. 

         many [i], pulls input from step 2a.

         = new_sum_A (2) += many[i (*when: 1)] = new_sum_B = 6

2d. printf("sum %d\n", sum)

         // “sum (new_sum_B)” = Output B: sum 6

2e. i++ = (i=1) + 1 = 2

         // i=2

——————————————————————————————————

Loop 3:

3a. i=2

3b. i (2) < 3

         // 2 is less than 3, loop continues.

3c. sum += many[i]

         // translation, everything in parenthesis. 

         many [i], pulls input from step 3a.

         = new_sum_B (6) += many[i (*when: 2)] = new_sum_C (14) 

3d. printf("sum %d\n", sum)

         // “sum (new_sum_C)” = Output C: sum 14

3e. i++ = (i=2) + 1 = 3

         // i=3

——————————————————————————————————

(non) Loop 4:

4a: i=3

4b. i (3) < 3

         // 3 is not less than 3, loop stops.

——————————————————————————————————

sum 2 sum 6 sum 14