C plus plus program to find prime number? - Answers

Here's an example. I've included analysis. #include<stdio.h> #include<stdlib.h> #include<math.h> int main(void) { /* User inputs high and low ends of range to search. / This could easily be done as function inputs, if / if so desired. */ int testprime,testdivisor, minprime, maxprime; printf("Search for primes between:\nLow end: "); scanf("%d",minprime); printf("Top end: "); scanf("%d",maxprime); int isprime; // 0 indicates a number is not prime.. for(testprime=minprime;testprime<=maxprime;testprime++) { isprime = 1; for(testdivisor=2;testdivisor<sqrt(testprime);testdivisor++) // Primes divide by 1! { isprime = testprime%testdivisor; // % finds remainders, so 7%3 returns 1. // If 0 is returned, a divisor has been found. if(isprime == 0) break; // Hence, not prime. "break;" exits the loop. } if(isprime != 0) printf("%d is prime.\n",testprime); } system("pause"); return 0; }