C Language Study Notes

1. logical operator | & if the subexpression on the left of the operator determines the final result, the subexpression on the right will not be calculated, for example, if (d! = 0 & n/d> 0) {/* average is greater than 0 */} if (p = NULL | * p = '\ 0 ') {/* no string */} in the first example, if there is no short circuit, once d = 0, the expression on the right will be divided by 0-the system may crash; in the second example, if p is a null pointer, the expression on the right references an empty address, which may cause system crash. 2. There is no uniform rule on the order of values of real parameters in C language. However, the order of values of function parameters in most systems is from right to left. I = 3; printf ("% d, % d \ n", I, I ++); the output result is: 4, 3, I ++ and ++ I operators I = 3; j = (++ I) + (++ I ); printf ("j = % d, I = % d \ n", j, I); the output result is: j = 16, I = 6 (gcc compiler) Different compilers, the results may be different. When computing j = (a + B) + (c + d) + (e + f), the computer first calculates (a + B) + (c + d ), and store the results (for example, stored in j), and then compute j + (e + f) = j; the computer only has one I. When the second I is calculated, the first I has changed. Int I = 1, j = 1, k; I = (I ++) + (++ I); k = (j ++) + (++ j ); printf ("I = % d, j = % d, k = % d \ n", I, j, k); output result: I = 5, j = 3, k = 4 (gcc compiler)