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Converting to ANSI C

Many K&R C programs compile with an ANSI C compiler without changes. Where changes are required, the compiler will nearly always tell you. A list of differences between K&R C and ANSI C is in [7]. The most important are

Function prototyping :-

Function prototypes aren't mandatory in ANSI C, but they improve error checking. Their use enables certain ANSI C features which otherwise, for backward compatibility, are suppressed.

Parameter Passing :-

• Floats are passed as floats (in K&R C floats are converted to doubles when passed to a function)

• Arguments are automatically cast into the right form for the called function. Without the function prototyping the following program wouldn't work because `mean' is expecting 2 integers.

  #include <stdio.h>
  #include <stdlib.h>
  
  int mean(int a,int b)
  {
    return a + b;
  }
  
  main()
  {
  int i;
  float f;
  int answer;
  
     i = 7;
     f= 5.3;
  
     /* deliberate mistake! */
     answer = mean(f,j);
     printf("%f + %d = %d\n", f, j, answer);
  }
  

Standardisation :-

The standard include files for ANSI C are

assert.h	Assertions
ctype.h	Character identification
errno.h	Error handling
float.h	Max and Min values for floats
limits.h	limits for integral types
locale.h	Internationalisation info
math.h	Advanced math functions
setjmp.h	Non-local jump
signal.h	Exception handling
stdarg.h	Variable numbers of arguments
stddef.h	Standard definitions
stdio.h	Input/Output
stdlib.h	General Utilities
string.h	String Manipulation
time.h	Date and Time functions

If you want to support both ANSI C and K&R C , you can use the following construction

#ifdef __STDC__
 /* ANSI code */
#else
 /* K and R code */
#endif