Give me an integer and I will sum it with the previous natural numbers

How to write a C Program Give me an integer and I will sum it with the previous natural numbers in C Programming Language ?

This C Program Change an Integer Number with Addition of Previous Natural Numbers.
 
Solution:

1. #include <stdio.h>
2. #include <stdlib.h>
3. int geometric_sum (int a);
4. int main ()
5. {
6.     int a = 0, sum = 0;
7.     printf("Give me an integer and I will sum it with the previous natural numbers : ");
8.     scanf("%d", &a);
9.     sum = geometric_sum(a);
10.     printf("Result: %d", sum);
11. }
12.  
13. int geometric_sum (int a)
14. {
15.     if (a == 0)
16.     {
17.         printf("Base case!\n");
18.         return a;
19.     }
20.  
21.     else
22.     {
23.         printf("1: sum (%d)\n", a);
24.         return a + geometric_sum(a-1);
25.     }
26.  
27. }

C Program That in a Given Natural Number x Insert Figure c at Position p

How to Write a program that in a given natural number x insert figure c at position p . The numbers x , c and p are entered from standard input . 

For example , x = 140 , c = 2 , p = 2 , the result is the 1420th


Solution:

1. #include<stdio.h>
2. #include<math.h>
3. 
   
4. int main() {
5.         int x,c,p,i,y,d;
6.         scanf("%d%d%d", &x,&c,&p);
7.         printf("Number: %d, figure %d, required position: %d\n", x,c,p);
8.         i=1;   
9.         y=10;  
10.         if(i==p){
11.                 x=x*10;
12.                 x=x+c;
13.                 printf("X: %d\n", x);
14.         }
15.         while(i<p){
16.         i++;
17.         c=c*10;
18.                 if(i==p){
19.                 d=x%y;
20.                 x=x-d;
21.                 x=x*y;
22.                 x=x+c+d;
23.                 printf("X: %d\n", x);  
24.                 }
25.         y=10*y;
26.         }
27.                
28.  
29.         return 0;
30. }