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Solved Examples · Example 32

Q.Write a C program to print the sum of the first 60 natural numbers. The textbook presents this worked program, transcribed exactly as printed (including its printed errors):
#include <stdio.h>  
void main()  
{  
int num, sum = 0  
for (num=1; num<=60; num++)  
sum=sum+num;  
printf("sum=%4d\n", sum);  
} /*End of main()*/  
Sample output printed in the textbook:
Sum = 1830  

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[!TLDR]

A for loop accumulates 1 + 2 + ... + 60 = 1830.

The for statement packs the three loop-control pieces into one header: for(initialise; test; update). Here num = 1 initialises the counter, num <= 60 is checked before each pass, and num++ advances it afterwards, so the single body statement sum = sum + num runs exactly 60 times. The closed-form check n(n+1)/2 gives 60 x 61 / 2 = 1830. …

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