why there is an error

Question

#include <iostream>
using namespace std;

int main(int argc, const char * argv[]) {
// insert code here...
string values[]={"hello", "world", "int",0};
for(int i = 0;string c = values[i];i++,cout<<c){}
return 0;
}

No viable conversion from 'std::__1::string' (aka 'basic_string<char>') to 'bool'. // why there is a error and what does the "No viable..." mean

Answer 1

The compiler is complaining about how confusing and basically impossible it is to interpret "string c = values[i]" as true or false.

That compiler problem is also related to a weird thing before it explained below.

The 0 in this line is very weird:
string values[]={"hello", "world", "int",0};

A null-terminated char array or c-style string is common where a '\0' char marks the end but if you want a null-terminated array of strings, you should write that differently. An array of string* could work but use nullptr or NULL. Don't treat 0 like it is a type of pointer.

If you want to represent length of an array in c++, you probably want a vector instead.
Another technique is what c conventionally does and the main function's command-line arguments are passed this way. In c, you'd pass the length as an int along with the array. argc and argv paramaters to main work like that.

Answer 2

The error simply says that your condition of *for* loop ( i.e. "string c = values[i]" ) can't be converted to Boolean type ( means can't be answered in YES or NO )

so your compiler didn't knew what to do there and threw an error complaining you the same.