C Program to find Prime Number using UDF, also find Prime Numbers upto a limit in C Language: Example 1 : C Program to find prime number using user defined function :- #include<stdio.h> #include<conio.h> int primeNumber(int); /* function declaration or prototype, int arg int returns */ void main() { int num,prime; clrscr(); printf("Enter an integer Number :"); scanf("%d",&num); prime = primeNumber(num); /* function call here with Actual Parameter num, rtns integer value and assigning to the var prime */ if(prime==1) printf("%d is a prime number",num); else printf("%d is not a prime number",num); getch(); } int primeNumber(int n) /* function definition with Formal Parameter n and returns an integer */ { int i; for( i=2 ; i<=n/2 ; i++) { if(n%i==0) return 0; } return 1; } /* prime number 3,7,11,17.... */ Example 2 : C Program to find prime num...