1. Control statement

It is used to control the execution flow of the program to realize various structural modes of the program. They are composed of specific statement definer. C language has nine control statements.

It can be divided into the following three categories:

• Conditional judgment statements are also called branch statements: if statements and switch statements;
• Circular execution statements: do while statement, while statement and for statement;
• Turn statements: break statements, goto statements, continue statements, and return statements.

2. Branch statement (select statement)

2.1 if statement

2.1.1 single branch statement

#include <stdio.h>
int main()
{
	int age = 0;
	scanf("%d", &age);

	if (age >= 18)
		printf("adult\n");
	return 0; 
}

2.1.2 double branch statement

#include <stdio.h>
int main()
{
	int age = 0;
	scanf("%d", &age);

	if (age >= 18)
		printf("adult\n");
	else
		printf("under age\n");
	return 0; 
}

2.1.3 multi branch statements

#include <stdio.h>
int main()
{
	int age = 0;
	scanf("%d", &age);

	if (age >= 18)
		printf("adult\n");
	else if (age >= 18 && age < 30)
		printf("youth\n");
	else if (age >= 30 && age < 50)
		printf("middle age\n");
	else if (age >= 50 && age < 80)
		printf("Middle aged and elderly");
	else if (age >= 80 && age < 100)
		printf("old age\n");
	else
		printf("God of Longevity\n");
	return 0; 
}

Note: if is followed by a statement by default. If you want to output multiple statements, you need to add {....}

2.1.4 suspended else

#include <stdio.h>
int main()
{
	int a = 0;
	int b = 2;
	if (a == 1)
		if (b == 2)
			printf("heh\n");
	else
			printf("haha\n");
}

Note: else matching: else matches the nearest if. So the output of this program does not execute if else.. Statement, no output.

2.1.5 judge whether a number is odd

#include <stdio.h>
int main()
{
	int n = 0;
	scanf("%d", &n);
	if (n % 2 == 1)
		//if(n%2!=0)
	{
		printf("Odd number\n");
	}
	return 0;
}

2.1.6 odd number between output 1 and 100

//Method 1
#include <stdio.h>
int main()
{
	int i= 1;
	while (i <= 100)
	{
		printf("%d ", i);
		i=i+2;
	}
	return 0;
}

//Method 2
#include <stdio.h>
int main()
{
	int i= 1;
	while (i <= 100)
	{
		//Judge i and print it only if it is an odd number
		if(i%2==1)
		printf("%d ", i);
		i++;
	}
	return 0;
}

2.2 switch statement

The switch statement is also a branch statement, which is often used in the case of multiple branches