C-#undef .

In this session i have discussed #undef preprocessor in C .

The #define preprocessor directive is used to undefine constant or macro that already declared by using #define in program .


#undef identifier value

Example : Write a program that demonstrate the use of #undef .

    #define PI 3.14
    #undef PI
    int main()
        int r;
        float area;
        printf("Enter the radious");
        printf("Area : %f",area);
        return 0;
    OUTPUT : error PI undeclared

In the above code i have define the PI as macro . But use of #undef i have undeclared the PI in this program .

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