The program adds first N natural numbers (starts from 1) and prints the sum in the console. We wrote this program using Dev C++ version 4.9.9.2 on a Windows 7 64-bit system. You may try other standard C compilers to run the program with modifications.
Learn following c programming concepts before you attempt this example program.
- C Assignment Operators
- C Arithmetic Operators
- C Reading Input Values
- C Printing Output Values
- C For Loop
Contents
Problem Definition
Natural numbers are all positive numbers greater than number 0 and it does not include the number zero.
For example
Natural\hspace{2mm} numbers = 1, 2, 3, 4, 5, \cdots
This C program reads the value of number N which is a natural number and then sum all other natural numbers up to number N start from 1. Suppose then
Sum = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 = 55
Flowchart Sum of First N Natural Numbers
Program Code Sum of First N Natural Numbers
/* Program for sum of First N Natural Numbers */ #include <stdio.h> #include <stdlib.h> main() { int num,i,sum; sum = 0; /* read the number */ printf("Enter number to sum:"); scanf("%d",&num); for(i=1;i<=num;i++) { sum = sum + i; } printf("sum of %d number is %d\n",num,sum); getch(); return 0; }
The most important piece of code in the above example is the for loop.
for ( i = 1; i <= num; i++) { sum = sum + 1; }
The for loop starts from 1 and goes through each digit between 1 and num because variable i is incremented with each iteration ( i++
). The value of num is user input and it can be a large number.
The value of i is added to variable sum using the following statement. The value of sum also increments with each iteration of the variable i in the for loop.
sum = sum + i;
The final value of the sum is printed as output.
Output
How many numbers to add?:10 ------------------------ sum of 10 number is 55 ------------------------