how to sum all numbers under a given number c 2b 2b

1int x, s = 0;
2   cout << "Enter the number : ";
3   cin >> x;
4   while (x != 0) {
5      s = s + x % 10;
6      x = x / 10;
7   }

1// Method 1: Mathematical -> Sum up numbers from 1 to n 
2int sum(int n){
3	return (n * (n+1)) / 2;
4}
5
6// Method 2: Using a for-loop  -> Sum up numbers from 1 to n 
7int sum(int n){
8	int tempSum = 0; 
9  	for (int i = n; i > 0; i--){
10     	tempSum += i;  
11    }
12  	return tempSum; 
13}
14
15// Method 3: Using recursion -> Sum up numbers from 1 to n 
16int sum(int n){
17	return n > 0 ? n + sum(n-1) : 0; 
18}

1// Method 1: Mathematical -> Sum up numbers from 1 to n 
2int sum(int n){
3	return (n * (n+1)) / 2;
4}
5
6// Method 2: Using a for-loop -> Sum up numbers from 1 to n 
7int sum(int n){
8	int tempSum = 0; 
9  	for (int i = n; i > 0; i--){
10     	tempSum += i;  
11    }
12  	return tempSum; 
13}
14
15// Method 3: Using recursion -> Sum up numbers from 1 to n 
16int sum(int n){
17	return n > 0 ? n + sum(n-1) : 0; 
18}

1#include <iostream>
2#include <math.h>
3// "#include <math.h> isn't needed.
4using namespace std;
5/* run this program using the console pauser or add your own getch, system("pause") or input loop */
6
7int main(int argc, char** argv) {
8	// Sum of numbers in a group under a given number.
9	cout << "Insert four numbers:" << endl;
10	// In this case the numbers I chose to use are four but you can use how many you want.
11	float a, b, c, d;
12	cin >> a >> b >> c >> d;
13	float aa, bb, cc, dd;
14	// The second set of variables must have the same number of variables of the numbers
15	// you want to sum.
16	if(a < 8){
17	// In this case "n" is replaced by 8, but, again, you can use any number you prefer.
18		aa = a;
19		if(b < 8){
20			bb = b;
21			if(c < 8){
22				cc = c;
23				if(d < 8){
24					dd = d;
25				} else {
26					dd = 0;
27				}
28			} else {
29				cc = 0;
30				if(d < 8){
31					dd = d;
32				} else {
33					dd = 0;
34				}
35			}
36		} else {
37			bb = 0;
38			if(c < 8){
39				cc = c;
40				if(d < 8){
41					dd = d;
42				} else {
43					dd = 0;
44				}
45			} else {
46				cc = 0;
47				if(d < 8){
48					dd = d;
49				} else {
50					dd = 0;
51				}
52			}
53		}
54	} else {
55		aa = 0;
56		if(b < 8){
57			bb = b;
58			if(c < 8){
59				cc = c;
60				if(d < 8){
61					dd = d;
62				} else {
63					dd = 0;
64				}
65			} else {
66				cc = 0;
67				if(d < 8){
68					dd = d;
69				} else {
70					dd = 0;
71				}
72			}
73		} else {
74			bb = 0;
75			if(c < 8){
76				cc = c;
77				if(d < 8){
78					dd = d;
79				} else {
80					dd = 0;
81				}
82			} else {
83				cc = 0;
84				if(d < 8){
85					dd = d;
86				} else {
87					dd = 0;
88				}
89			}
90		}
91	}
92	cout << endl << "Sum of the numbers lower than n (8): " << aa+bb+cc+dd << endl;
93	// Basically this associates each number to a variable of the second group and
94	// then, through if, it sees which numbers are under n.
95	// If they are under n the second variable is given the same numeric value as
96	// its respective number, if not its value is equal to 0.
97	// It then sums the variables together.
98	// To have more/less numbers you add the respective variables, then make two
99	// cases where the number is higher or lower than n. Then, you copy-paste
100	// the two if chains underneath.
101	return 0;
102}