Summary of error prone knowledge points: Calculation of define s (x) 3*x*x+1.

This is a macro definition with parameters , Usually, the macro parameters in the macro content text are replaced with text .
Let's use this to write an example for calculation .

#define SUM(x) 3*x*x+1

int main()
{
    
    int i=5;
    int j=8;
    printf("%d\n",SUM(i+j));
}

The answer from the computer is 64.

My wrong idea at the beginning is ：
3*(5+8)*(5+8)+1.
But the difference between the calculated value and the actual value .

The right thinking is ：SUM Don't put parentheses Take it with you , Only the formula Take it to .
3*5+8*5+8+1.
The calculated answer is exactly the same as the actual answer .