Difference Between C and ANSI C - A Clear and Simple Comparison

What Is the C Programming Language?

C was created in the early 1970s by Dennis Ritchie at Bell Labs. It quickly became popular because it offers:

• Close-to-hardware programming abilities
• Simple syntax
• High efficiency

However, without a standard, different compilers had varying implementations of prototype C programming, making code sharing difficult and reducing portability.

What Is ANSI C?

To solve these problems, the American National Standards Institute (ANSI) developed a standardized version of C in 1989. This standard is often called ANSI C, C89, or C90 (the ISO standard that followed shortly after).

ANSI C isn’t a new language; it’s a formal standard that refines and extends the original C. It ensures consistent behavior across compilers and platforms.

Key Differences Between C and ANSI C

Both versions share the same roots, but ANSI C programming adds more structure, stricter rules, and greater portability.

1. Standardization and Portability

• C: Different compilers had varying implementations, causing portability problems.
• ANSI C: Introduced a uniform standard that every ANSI C compiler follows.

2. Function Prototypes

• C: Functions could be declared without specifying parameters, which sometimes led to runtime errors.
• ANSI C: Requires function prototypes, allowing type mismatches to be caught early.

// Old C-style function declaration (no parameter details)
int add();

// ANSI C style function prototype (parameters specified)
int add(int a, int b);

3. New Keywords and Data Types

ANSI C programming added:

• const – Declares variables as read-only to prevent accidental changes.
• void – Represents no value or no parameters, improving clarity.
• wchar_t – Supports wide characters for internationalization.

4. Stricter Type Checking

ANSI C enforces stronger rules on type conversions and promotions, reducing bugs caused by implicit conversions.

5. Improved Input/Output Functions

ANSI C added more flexible I/O functions like fprintf() and fscanf(), enhancing file and stream handling.

6. Header Files and Libraries

While many standard headers existed before, ANSI C standardized and expanded them, supporting new functions and features.

7. Preprocessor Enhancements

New directives such as #error and #pragma were introduced in ANSI C, giving programmers better control over compilation and error handling.

8. Error Handling

ANSI C formalized error handling with the errno variable and , making runtime error detection more consistent.

C vs ANSI C – Code Examples

Let’s look at a simple addition program written in both the original C style and the ANSI C style to understand the difference in function declaration and usage.

Example 1: Old C-Style Function Declaration

#include 

// Function declared without specifying parameters
int add();

int main() {
    int result = add(10, 20);
    printf("Sum: %d\n", result);
    return 0;
}

// Function definition with parameters
int add(a, b)
int a;
int b;
{
    return a + b;
}

Example 2: ANSI C-Style Function Prototype

#include 

// Function prototype with parameters specified
int add(int a, int b);

int main() {
    int result = add(10, 20);
    printf("Sum: %d\n", result);
    return 0;
}

// Function definition matching the prototype
int add(int a, int b) {
    return a + b;
}

In the original C style, parameters were not part of the function declaration, which could cause runtime errors if mismatched types were passed. ANSI C fixes this by enforcing function prototypes, allowing the compiler to catch type errors before running the program.

Why Is ANSI C Important?

Summary of improvements in ANSI C:

• Makes code more portable across different hardware and compilers
• Encourages better programming practices with function prototypes and strict typing
• Supports modern programming needs with new data types and improved libraries

Because of these benefits, ANSI C remains the foundation of C programming today.

Summary Table – C vs ANSI C

Conclusion

Knowing the difference between C and ANSI C is important for anyone working with the C language today. Original C created the base, but ANSI C made it stronger, more portable, and safer. Whether maintaining legacy projects or building new software, following ANSI C compiler standards ensures reliability and compatibility.