C Language / Preprocessor Directives
These Statements which are executed before compilation. Preprocessor Directives are statements which start with # symbol. These are used for 3 purpose.They were
1. Macro Variable.
2. Macros Function.
3. Conditional compilation.
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Preprocessor Directives Uses
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Example
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Macro defines a constant value
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#define pi 3.14
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Header file inclusion for a library
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#include<filename>
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Conditional compilation for including or excluding in source program before
compilation with respect to the condition.
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set of commands like #ifdef, #endif, #if, #else, #ifndef are used in programs
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Process of Preprocessing
Source code -->Preprocessor-->Expanded source code -->compiler Program.
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Preprocessor Directives
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Program
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Output
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Macro Variable
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#include <stdio.h>
#define Pivalue 3.1415
void main()
{
printf("Pi value=%.f",Pivalue);
}
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Pi value=3
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Macros Function
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#include <stdio.h>
#define sq(r) (r*r)
void main() {
printf("Square Value of 3 = %d", sq(3));
}
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Square Value of 3 = 9
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Conditional compilation
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#include<stdio.h>
#define a 20
#define b 10
void main()
{
#if (a>b)
printf("a is bigger than b");
#else
printf("b is bigger than a");
#endif
}
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a is bigger than b
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