C language selection, loop overview

Select statement

Common logical operators

if

#include <stdio.h>int main(){	int a;	scanf("%d", &a);	if (a > 1)		printf("a Greater than 1");	return 0;}

if…else…

Implementation of conditions if What's in the sentence , Otherwise execution else Later

#include <stdio.h>int main(){	int a;	scanf("%d", &a);	if (a >= 60)		printf(" pass ");	else		printf(" fail, ");	return 0;}

if…else if…else

It is not difficult to guess by comparing the above ,
If … And if … otherwise …

#include <stdio.h>int main(){	int a;	scanf_s("%d", &a);	if (a >= 60 && a <= 70)		printf(" pass ");	else if (a > 70 && a <= 80)		printf(" good ");	else if (a > 80)		printf(" good ");	else		printf(" fail, ");	return 0;}

expression 1？ expression 2： expression 3

It means when expression 1 When it's true , Execute expression 2, Otherwise, execute the expression 3

#include<stdio.h>int main() {	char ch;	scanf("%c",&ch);	ch = (ch >= 'A' && ch <= 'Z') ? (ch + 32) : ch;	printf("%c", ch);	return 0;}

switch sentence

swtich( expression )  {    // () Only integers are supported for data types in                  case  Constant 1 :                    Statement to execute ;                   break;                 case  Constant 2 :                    Statement to execute ;                   break;                 case  Constant 3 :                    Statement to execute ;                    break;                 default:                    Statement to execute ;                   break;}

Be careful ：default, When the above conditions are not met , perform default sentence

Example

1. Judgement of leap year
2. Determine whether the character is a capital letter , If lower case letters are converted to upper case , Otherwise direct output （ See the conditional expression code above ）

// Leap year #include<stdio.h>int main() {	int y;	scanf_s("%d", &y);	if ((y % 4 == 0 && y % 100 != 0) || y % 400 == 0) {		printf("%d It's a leap year ", y);	}	else {		printf("%d It's not a leap year ", y);	}	return 0;}

Loop statement

for

Imagine an operation , We define an array size as 10, And then you're going to put data into this array ,

int a[10];a[0]=1;a[1]=2;......a[9]=10;

for(int i=0;i<10;i++){	a[i]=i+1;}

int i=0; Is the initial condition of the cycle
i<10; Is the cyclic condition , When i<10 The cycle continues
i++;i Self increment per cycle 1

i++,++i

i++, Perform the operation first , Since the increase again
++i, First of all, increase by yourself , Perform the operation again

while and do……while

while loop ：

while The key point of the loop is The loop may not execute once . When conditions are false when , Will skip the body of the loop , Direct execution followed by while The next statement of the loop .

#include <stdio.h> // Output 0-9int main (){   int a = 0;   while( a < 10 )   {      printf("a  Value ： %d\n", a);      a++;   }   return 0;}

And while The difference in the cycle is ：
do…while Loop at least once

#include <stdio.h>int main (){   int a = 0;   do   {   		printf(" Although I don't meet the conditions , But do it again ");   	}while(a>0);   return 0;}

Example ：

Suppose the user's password is a three digit integer , Make the user enter the password , If the input is successful , Prompt welcome, If input fails , Prompt ”bad password“, If the input fails three times , Then lock , Tips ：“user locked”

#include <stdio.h>int main(){	int key = 123;	int times = 0;// frequency 	bool passed = 0;	do	{		times++;		int input = 0;		printf(" Please input a password ：");		scanf_s("%d", &input);		if (key == input)		{			passed = 1;			break;		}		else		{			printf("bad password\n");		}	} while (times < 3);	if (passed)	{		printf("Welcome");	}	else	{		printf("user locked");	}	return 0;}

function

I'm not going to say much , Function declaration Correct the wrong questions , Multiple choice questions ！

Declaration of functions （ C The function prototype ）, Tell the compiler the type of the function , And you need to find the definition of this function elsewhere .
Definition of function , The concrete realization of function , It specifies the specific functions of the function .
Function call , Causes the function to be executed .
The function must Declare before use . Function definition before calling , Don't say , Function definition after call or in other files , You must declare before calling . The called function declaration can be outside the calling function , You can also place variable declarations anywhere in the calling function .

Let's define a function that returns the maximum value

int max(int num1, int num2) {   int result;    if (num1 > num2)      result = num1;   else      result = num2;    return result; }

Function declaration

int max(int num1, int num2);

Function call

#include <stdio.h> /*  Function declaration  */int max(int num1, int num2); int main (){   /*  Definition of local variables  */   int a = 100;   int b = 200;   int ret;    /*  Call the function to get the maximum value  */   ret = max(a, b);    printf( "Max value is : %d\n", ret );    return 0;} /*  The function returns the larger of the two numbers  */int max(int num1, int num2) {   /*  Local variable declaration  */   int result;    if (num1 > num2)      result = num1;   else      result = num2;    return result; }

Last

And the structure , The pointer , I'm not going to talk about , Given the difficulty , If you still need to strengthen your study , Welcome to the blogger column , Best wishes ： Everyone, learn from the scum ,c Language must pass ！！！