M's C memo - branch and loop statements

Control statements are used to control the execution process of the program to realize various structural modes of the program. They are composed of specific statement definer. There are nine kinds of control statements in C language.

It can be divided into the following three categories:

1. Conditional judgment statements are also called branch statements: if statements and switch statements;

2. Circular execution statements: do while statement, while statement and for statement;

3. Turn statements: break statements, goto statements, continue statements, and return statements.

2. Branch statement (select structure)

2.1 if statement

Syntax structure:

//Single branch
    if(expression)
       sentence;


    if(expression)
       Statement 1;
    else
       Statement 2;

//Multi branch
    if(Expression 1)
       Statement 1;
    else if(Expression 2)
       Statement 2;
    else
       Statement 3;

Else matching: else matches the nearest if.

2.2. switch statement

switch is a multi branch statement

switch(Integer expression)
{
   case Integer constant expression:
    sentence;
}

2.2.1 break in switch statement

The switch statement needs to be combined with break to realize the real branch

#include <stdio.h> 
int main() 
{    
    int day = 0;    
    switch(day)   
    {        
        case 1:             
            printf("Monday\n");
            break;        
        case 2:            
            printf("Tuesday\n");
            break;
        case 3:
            printf("Wednesday\n");
            break;            
        case 4:
            printf("Thursday\n");
            break;            
        case 5:
            printf("Friday\n");
            break;        
        case 6:
            printf("Saturday\n");
            break;
        case 7:
            printf("Sunday\n");
            break;
    }
    return 0;
}

When required:

1. Input 1-5 and output "weekday";

2. Input 6-7 and output "weekend"

So our code should be implemented in this way:

#include <stdio. h> / / switch code demonstration 
int main() 
{    
    int day = 0;
    switch(day)
    {
        case 1: 
        case 2:
        case 3:        
        case 4:
        case 5:
            printf("weekday\n");
            break;
        case 6:
        case 7:
            printf("weekend\n");
            break;
   }
   return 0;
}

The actual effect of the break statement is to divide the statement list into different branch parts.

Good programming habits

Add a break statement after the last case statement.

(this is written to avoid forgetting to add a break statement after the last previous case statement.).

2.2.2ddefault clause

When all case conditions are not met, the default statement is executed

3. Circular statement

3.1. while cycle

while syntax structure

while(expression)
    Circular statement;

The process of executing the while statement:

Print numbers from 0 to 10 on the screen.

#include<stdio.h>
int main()
{ 
    int i = 0; 
    while(i<=10) 
    { 
        printf("%d ", i); 
        i = i+1;
    }
    return 0;
}

3.1.1 break and continue in while

break: jump out of the whole loop

continue: skip a loop

3.2 for cycle

3.2.1 grammar

for(Expression 1; Expression 2; Expression 3)

    Circular statement;

Expression 1

Expression 1 is the initialization part, which is used to initialize the of the loop variable.

Expression 2

Expression 2 is a condition judgment part, which is used to judge the termination of the cycle.

Expression 3

Expression 3 is the adjustment part, which is used to adjust the loop conditions.

Execution process of for loop

3.2.2. break and continue in the for loop

Same as while loop

3.2.3 loop control variable of for statement

1. Do not modify the circulation variable in the circulation body to prevent dead circulation

2. Adopt the interval writing method of front closing and rear opening

for(i=0;i<10;i++) 
{}

3.2.4 variants of the for loop

#include <stdio.h> 
int main() 
{ 
    for(;;) 
    { 
        printf("hehe\n"); 
    }    
    //The initialization part, judgment part and adjustment part of the for loop can be omitted, but it is not recommended to omit them at the beginning of learning, which is easy to cause problems.     return 0; 
}

3.3do... while() loop

3.3.1 grammar

do
    Circular statement;
while(expression);

3.3.2 implementation process

3.3.3 characteristics of do statement

Execute the loop body once first

3.3.4 break and continue

Same as for loop

4. goto statement

Syntax format:

again:

goto again;

Usage scenario:

Jump out of multi-layer loop

Topics: C Back-end

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