`gets()` in C is considered unsafe because it can lead to buffer overflow vulnerabilities. This happens when the function doesn't check if the input exceeds the allocated memory buffer.

Key Issue: If the input exceeds the size of the buffer, it overwrites other memory regions, which can cause undefined behavior, crashes, or security vulnerabilities like stack corruption.

If you declare a buffer of size 10 but the user enters 20 characters, gets() will allow writing past the buffer’s boundary, which causes overflow.

char buffer[10];
gets(buffer);  // Dangerous if input is more than 10 characters
                

In the above example, the input exceeds the buffer's allocated size, leading to undefined behavior or memory corruption.

In C, a safer alternative to `gets()` is `fgets()`, which allows you to specify the buffer size, preventing overflow.

char buffer[20];
fgets(buffer, sizeof(buffer), stdin);  // Safer than gets()
                

In this example, `fgets()` ensures that no more than `sizeof(buffer)-1` characters are read, including the null-terminator.

`readln()` in Pascal automatically handles input size by reading data into a variable that has a fixed size. It prevents buffer overflow because the input is constrained to the variable’s type and size.

If you declare a variable as string[20], `readln()` will ensure that only 20 characters are accepted, discarding any excess input.

program SafeInput;
var
  name: string[20];
begin
  writeln('Enter your name:');
  readln(name);  // Only up to 20 characters will be accepted
  writeln('Hello, ', name);
end.
                

This makes Pascal's `readln()` more predictable and secure compared to `gets()` in C.

• Bounds Checking: In Pascal, `readln()` is tied to the size of the variable, preventing overflow, while `gets()` in C does not check the buffer size.
• Error Handling: Pascal performs bounds checking automatically, while in C, you must handle it manually (e.g., using `fgets()`).
• Memory Management: Pascal enforces size limits, while C provides more control but requires careful management of memory.

In summary:

• Pascal's `readln()` is safer than C's `gets()` because it handles bounds checking automatically.
• In C, use `fgets()` instead of `gets()` to avoid buffer overflow vulnerabilities.
• When writing code, always consider input size limitations to protect against security risks.