Thought I'd test my programming skills by making a program which tells you the prime factorisation of a number or range of numbers. i.e:
4 = 2 x 2
10 = 2 x 5
20 = 2 x 2 x 5
etc...
Here's the code which works it out for a series of numbers:
//
// main.c
// printInPrimeFactors
//
// Created by Monkey on 10/03/2013.
// Copyright (c) 2013 Monkey. All rights reserved.
//
#include
#define TRUE 1
#define FALSE 0
int isPrime (int number);
int printInPrimeFactors (int number);
int main(int argc, const char * argv[])
{
//scan in a number
int startNumber = 0;
printf("Type a starting number: ");
scanf("%d", &startNumber);
int endNumber = 0;
printf("Type an end number: ");
scanf("%d", &endNumber);
//find the prime factors of range of numbers
for (int i=startNumber; i<=endNumber; i++) {
printInPrimeFactors(i);
}
return 0;
}
int printInPrimeFactors (int number) {
//printf("finding the prime factors of %d.....\n", number);
//if it's a prime just print it and return to main
if (isPrime(number)) {
printf("%d\n", number);
return 0;
}
//for nice formatting I'm printing the number =
printf("%d = ", number);
//testing to find a factor of the number, which is also prime
for (int i =2; i < number; i++) {
if (number %i == 0 && isPrime(i)) {
//printf("a prime factor of %d is %d\n", number, i);
//testing to see how many times the number can be divided by 'i' and printing i each time
//printf("testing to see how many times %d can divide by %d\n", number, i);
int result = number;
while (result % i == 0) {
printf("%d x ", i);
result = result / i;
}
//print an extra line to make it look nice
//printf("\n");
}
}
//print new line for next number
printf("1\n");
return 0;
}
//a function which returns true or false if number is prime
int isPrime (int number) {
//printf("testing to see if %d is a prime\n", number);
int prime = TRUE;
//test to see if it is divisible by any other numbers
for (int i = 2; i < number; i++) {
if (number %i ==0) {
prime = FALSE;
//printf("%d is not a prime number\n", i);
return prime;
}
}
return prime;
}
output:
Type a starting number: 100
Type an end number: 120
100 = 2 x 2 x 5 x 5 x 1
101
102 = 2 x 3 x 17 x 1
103
104 = 2 x 2 x 2 x 13 x 1
105 = 3 x 5 x 7 x 1
106 = 2 x 53 x 1
107
108 = 2 x 2 x 3 x 3 x 3 x 1
109
110 = 2 x 5 x 11 x 1
111 = 3 x 37 x 1
112 = 2 x 2 x 2 x 2 x 7 x 1
113
114 = 2 x 3 x 19 x 1
115 = 5 x 23 x 1
116 = 2 x 2 x 29 x 1
117 = 3 x 3 x 13 x 1
118 = 2 x 59 x 1
119 = 7 x 17 x 1
120 = 2 x 2 x 2 x 3 x 5 x 1
after all that
I found this nice website which basically does the same!
