# C Exercises: Sum of the digits equals to another given number

## C Basic Declarations and Expressions: Exercise-141 with Solution

Write a C program that reads n digits (given) chosen from 0 to 9 and prints the number of combinations where the sum of the digits equals another given number (s). Do not use the same digits in a combination.

For example, the combinations where n = 3 and s = 6 are as follows:

1 + 2 + 3 = 6

0 + 1 + 5 = 6

0 + 2 + 4 = 6

**Sample Solution:**

**C Code:**

```
#include<stdio.h>
// Recursive function to find combinations
int combination(int n, int s, int a) {
int i, result = 0;
// Base case: if n is 1, check if s is within valid range
if (n == 1) {
if (s >= a && s <= 9) {
return 1;
} else {
return 0;
}
}
// Iterate through possible values (a to 9)
for (i = a; i <= 9; i++) {
// Recursively call combination for (n-1) and adjust s and a values
result += combination(n - 1, s - i, i + 1);
}
return result; // Return the total combinations
}
int main() {
int n, s;
printf("Input the number:\n");
scanf("%d", &n);
printf("\nSum of the digits:\n");
scanf("%d", &s);
if (n != 0 && s != 0) {
printf("Number of combinations: %d\n", combination(n, s, 0));
}
return 0;
}
```

Sample Output:

Input the number: 3 Sum of the digits: 6 Number of combinations: 3

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