Why Does ISO C Forbid Comparing Pointers and Integers, and How Can I Fix This Error in My Code?

ISO C Comparison Error: Pointers and Integers

While working on an example from Bjarne Stroustrup's C book, some users have encountered a compile-time error indicating that ISO C forbids comparison between a pointer and an integer. This issue arises from a comparison involving a char variable and a string constant in the accept() function.

Cause:

The error occurs because ISO C prohibits direct comparison of a character pointer (such as char*) with an integer (such as the numerical value of a character enclosed in double quotes, e.g., "y").

Solutions:

There are two primary ways to resolve this error:

1. Preferable Approach: Using a String Variable:

   • Change the type of answer to string. This allows direct comparison with the string constant "y," resolving the issue.

   <code class="cpp">#include <iostream>
   #include <string>
   using namespace std;
   bool accept()
   {
       cout << "Do you want to proceed (y or n)?\n";
       string answer;
       cin >> answer;
       if (answer == "y") return true;
       return false;
   }</code>

2. Alternative Approach: Using Single Quotes:

   • If using a char variable is essential, enclose the character constant in single quotes to represent a char constant.

   <code class="cpp">#include <iostream>
   #include <string>
   using namespace std;
   bool accept()
   {
       cout << "Do you want to proceed (y or n)?\n";
       char answer;
       cin >> answer;
       if (answer == 'y') return true;
       return false;
   }</code>

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