c++ - Iteration counter not incrementing -

i wrote program in c++ print primes 100, writes "hello world", , hangs. why that?

#include <iostream>  bool is_prime(int num) {     if(num == 1)     {         return false;     }     for(int = 2; < num; i++)     {         if(num % == 0)         {             return false;         }     }     return true; }  int increase(int i) {     return i++; }  int main() {     std::cout << "hello world!!" << std::endl;     int = 1;     while(i < 100)     {         = increase(i);         if(is_prime(i))         {             std::cout << << " prime" << std::endl;         }     } } 

return i++; statement return original value of i, not incremented one.

you need return ++i; or return + 1 (thanks @interjay pointing that). later return + 1; makes clear return value matters, , not new value of i.

the effect of post increment i++ visible on next line (or usage of i).

not sure, if need separate method incrementing variable i, can @ in while loop.

 while(i < 100)     {          if(is_prime(i))         {             std::cout << << " prime" << std::endl;         }         i++;     } 

you can use for loop, instead of while since working range of values.

for(i = 1; < 100; i++) {     if(is_prime(i))     {         std::cout << << " prime" << std::endl;     } }