Sum of numbers using 2 functions - c

Question

Just learning C and I'm trying to understand how I get the sum of numbers using 2 functions but the results is incorrect.
I'm trying to ask the user for 10 numbers which are stored in an array in function main. The sum is then calculated in a separate function and then displayed in main.
Here is my original code without multiple functions that works:
int main()
{
int n[10];
int index;
int sum_n = 0;
int largest_n;
int smallest_n;
int *p;
p = &n[10];
int a;
printf("Enter 10 Integers\n");
for (index = 0; index < 10; index ++){
scanf("%d", &n[index] );
sum_n += n[index];
}
printf("The Sum of numbers is %d\n", sum_n);
}
Here is me trying to convert it to functions but the sum isn't working out:
int calculations (int);
int main()
{
int n[10];
int index;
int largest_n;
int smallest_n;
int *p;
p = &n[10];
int a;
printf("Enter 10 Integers\n");
for (index = 0; index < 10; index ++){
scanf("%d", &n[index] );
}
if (n[index] = 10){
//sum_n += n[index];
printf("The Sum of numbers is %d\n",calculations(n[index]));
}
&
int calculations (int num){
int sum_n = 0;
sum_n += num;
return sum_n;
}
When I run the second program using functions for numbers 1 to 10 I'm getting:
I'm either doing something blatantly wrong or not understanding what I'm doing at all.

Answer 1

every time you call a function the variables declared within a function are reset.
in case you want a variable that won't be reset every time you call a function you can simply make it static.
moreover you are passing and argument n[10] but your array stores number from n[0] to n[9] . And if you want sum of all ten numbers then you have to call calculation function for every number or you could just pass whole array. here is modified code.
#include<stdio.h>
int calculations (int);
int main()
{
int n[10];
int index;
int largest_n;
int smallest_n;
int *p;
p = &n[10];
int a;
int ans=0;
printf("Enter 10 Integers\n");
for (index = 0; index < 10; index ++){
scanf("%d",&n[index]);
ans = calculations(n[index]);
}
printf("The Sum of numbers is %d\n",ans);
}
int calculations (int num){
static int sum_n;
sum_n += num;
return sum_n;
}

Answer 2

First you don't need array for sum in this code, Second always remember to check what returned by scanf.The code is very simple.
first part with main
int main()
{
int n;
int sum=0;
printf("Enter 10 Integers\n");
for (int index = 0; index < 10; index ++){
if(scanf("%d", &n))
sum+=n;
}
printf("The Sum of numbers is %d\n",sum);//calculations(n));
}
Second using function calculation
int sum=0;
void calculation(int num){
sum+= num;
}
int main()
{
int n;
printf("Enter 10 Integers\n");
for (int index = 0; index < 10; index ++){
if(scanf("%d", &n))
calculation(n);
}
printf("The Sum of numbers is %d\n",sum);//calculations(n));
}

Answer 3

Your function calculations() simply returns its parameter (0 + num is simply num).
The statement
int sum_n = 0;
in it resets sum_n to 0 every time of calling it.
Move this statement out of it - directly into main() function (and before calling calculations()).

Answer 4

Corrections mentioned in comments below.
int calculations (int *num){ //Should be a pointer or array eg. int num[] as you want to pass an array to this function
int sum_n = 0;
int i;
//Create loop here to iterate over array and sum elements
for(i=0; i<sizeof(num)/sizeof(int); i++)
sum_n+=num[i];
return sum_n;
}
And
if (n[index] = 10){ //This is logically incorrect. This should be if(index==10).
// n[index]=10 will assign 10 to a[10] and if will still pass as if(10) is true but make a note of it. Don't use assignment operator inside if, you need comparison operator `==`
printf("The Sum of numbers is %d\n",calculations(n[index])); //You should call calculations like this -> calculations(n). You should pass whole array not just an element.
}