iOS Learning Notes---C language the next day

One, bool Boolean type C language does not have bool type, OC has bool type

is a non-true-and-false data type, with a Boolean type of variable that has only Yes and no two values. Yes indicates that the expression is true and no indicates that the expression is false.

In the C language, it is true that 0 is not.

The bool value is commonly used in branch statements to determine whether an if statement or an else statement is executed.

In a cyclic structure, it is also often used to determine whether a loop is to be executed using the BOOL value.

Precautions:

#define YES 1

#define NO 0

When the computer is recognized, yes is replaced by 1,no instead of 0.

Second, relational operators

> >= <= = = =!

Mainly used for comparison operation, the result of comparison is only true and false two cases, the result value is stored with BOOL type variable.

Note: Determine whether two numbers are equal with = = (double equals).

#import <Foundation/Foundation.h>

int Main (int argc, const Char * argv[])

{

BOOL A = 3 >6;

printf ("a =%d", a);

return 0;

}

BOOL can be seen as a smaller range of shaping, with only two numbers of 1 and 0.

Third, logical operators

An expression consisting of logical operators, and the result is not true or false

&& (Logic and): The result of the entire logical expression is true when the expression on both sides of the operator is true.

|| (logical OR): When the expression on both sides of the operator is false, the result of the entire logical expression is false. An expression | | An expression

！ (logical): Reverse the result of an expression.

Short Circuit phenomenon

&& the front is false, the back is not calculated directly to determine the false

Attention to logic and logic or short circuit phenomena

&&------A fake or fake

|| -------is True

Three structures of the program: sequential structure, branching structure, cyclic structure

Iv. If statement

Constructs a branching structure with an if statement, which determines the execution of a branch segment based on the conditions given.

The expression form of the IF statement in C language

1.if (conditional expression) {

Statement 1;

}

When the conditional expression is true, execute statement 1, otherwise skip statement 1 and proceed to the following statement.

eg