C pointer principle (69)-C Quick Start (2)

However, if we enter numbers such as 900 and-10 in the above program that do not meet the requirements,

Hello, please enter a number: 900

The number you entered is: 900

Hello, please enter a number:-10

The number you entered is-10.

The system does not prompt an error. Therefore, you need to modify the program to limit the range of players entering numbers.

# Include

Int main (){

Int mynum;

Printf ("hello, please enter a number :");

Scanf ("% d", & mynum );

If (mynum> 500 | mynum <1 ){

Printf ("the number is limited to 1-. Please run this program again! \ N ");

}

Else {

Printf ("\ n the number you entered is: % d \ n", mynum );

}

}

Run the program:

Dp @ dp :~ /Cquick % gcc guessnum. c-o myguess

Dp @ dp :~ /Cquick %./myguess

Hello, please enter a number: 200

The number you entered is: 200

Dp @ dp :~ /Cquick %./myguess

Hello, please enter a number: 900

The number is limited to 1-. Please run this program again!

Dp @ dp :~ /Cquick %

The above program uses the C language if... else... statement block, which is a mechanism available in many languages (including some functional languages, such as the if... then... else ....), the statement block consists of two parts: the first part of the if statement segment, which indicates that if the condition following the if statement is met, the if statement segment is executed, and the second part is the else statement segment, if the condition after if does not meet the execution condition, what is the condition and does not meet the condition? C language can be understood as if the return value of the condition is not 0, the condition is met, and if it is 0, the condition is not met.

You can combine multiple conditions into a comprehensive condition as the condition for the statement block by using | (represents or) or & (represents and), such as the conditions in the above program: mynum> 500 | mynum <1

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However, there is a keyword NULL in C. In C, the NULL and 0 values in the Condition Statement are the same, but NULL is often used for pointers and objects, 0 is commonly used in integer numbers such as int. This means that if the following similar statement blocks appear, it means that the pointer variable is contained (the pointer variable is usually used to point to the memory address of other variables, such as mypoint1 and mypoint2 in the following code) the following conditions are determined:

If (mypoint1! = NULL ){

............

}

If (mypoint2 = NULL ){

............

}

According to the running effect, the wrong number is not accepted, but to re-enter it, you must re-run the program.