CODEWITHSUNDEEP
csum
entropic.chaos
entropic.chaos

Reputation: 15

Issue with sum in for loop

Hi sorry this one may be a stupid question but I'm just moving my first steps in C and I couldn't find any specific answer, so:

Let's say I have to sum up some integers, why the expression sum += sum , in this code returns just only the last number I enter time 2 (lastNumber*2)?

unsigned int count = 0, sum = 0;
printf("How many numbers do you want to sum: ");
scanf("%u", &count);

for (int i = 1; i <= count; ++i) {
    printf("enter the integer: ");
    scanf("%u", &sum);
    sum += sum;
}

printf("the sum of all the %u numbers is: %u\n", count, sum);

PS: This problem is solved if I replace the expression with sum += x; But I can't understand why.

Upvotes: 0

Views: 71

Answers (4)

Ahmed Salah
Ahmed Salah

Reputation: 969

Because sum += sum; equivalent to sum = sum + sum; and (sum + sum) equivalent to (2 * sum).

Upvotes: 0

Jabberwocky
Jabberwocky

Reputation: 50775

You probably want this:

unsigned int count = 0, sum = 0;
printf("How many numbers do you want to sum: ");
scanf("%u", &count);

for (int i = 1; i <= count; ++i) {
    printf("enter the integer: ");
    unsigned int value;
    scanf("%u", &value);
    sum += value;  // or sum = sum + value;
}

printf("the sum of all the %u numbers is: %u\n", count, sum);

Upvotes: 0

yuvalhuck
yuvalhuck

Reputation: 23

When you doing scanf(..., &sum) you actually override its value. So, each iterate you doing nothing. Generally, it is good practice to dedicate variable to each purpose. Which means- variable contains the sum, and other one gets the user input.

Upvotes: 0

izlin
izlin

Reputation: 2138

With the line 

scanf ("%u", &sum); // Let's say the user enters "7"

you override the value of sum on every iteration with a new value entered by the user. Afterwards you add the user variable again with

sum = sum + sum;  // equivalent to sum = 7 + 7;

You can avoid that by using two variables:

int sum = 0;
int userIn = 0;
scanf ("%u", &userIn);  // userIn has now the value of the user input
sum += userin; // Add that value to the sum

Upvotes: 1

Related Questions