C language selection structure programming can be divided into two types of
single branch selection programming
single branch if statement format
if (expression)
statement 1;
//例子：(判断输出值)
#include <stdio.h>
int main(){
int a;
int b;
printf("请输入a，b，\n");
scanf("%d,%d",&a,&b);
if(a==b){
printf("是的！a=b时正确的！\n");
return 0;
}
}Multi-branch selection program design
Multi-branch selection structure has double-branch structure,
double-branch if statement format
if (expression) { statement 1; else statement 2; … }
//例子：（判断两个数的最大值）
#include <stdio.h>
int main(){
int a;
int b;
printf("input a,b:" );
scanf("%d,%d",&a,&b);
if (a>b)
{
printf("max=%d\n",a );
}
else{
printf("max=%d\n",b );
}
return 0;
}Multi-branch structure
1.
if (expression) { statement 1; else if () { statement 2; } } 2. else if statement if (expression) { statement else if (/* expression /){/ statement /} else if (/ expression /){/ statement*/} } else{statement}
//判断数字值代表的星期
#include <stdio.h>
int main(int argc, char const *argv[])
{
int a;
printf("please input your number" );
scanf("%d",&a);
if (a==1)
{
printf("Today is monday!\n");
}
else if (a==2)
{
printf("Today is tuerday\n" );
}
else if (a==3)
{
printf("Today is wednesday\n" );
}
else if (a==4)
{
printf("Today is thursday\n" );
}
else if (a==5)
{
printf("Today is firday\n" );
}
else if (a==6)
{
printf("Today is saturday\n" );
}
else if (a==7)
{
printf("Today is sunday\n" );
}
else{
printf("sorry ! your enter number is false! please input again! thanks\n" );
}
printf("It is good week!\n" );
return 0;
}例子（判断两个数值定义）
#include <stdio.h>
int main(){
char sex; /定义字符型数值sex/
int tall; /定义整型数值tall/
printf("请输入sex、tall数值");
scanf("%c%d",&sex,&tall); /输入sex tall的数值/
if(sex='F'){
/判断输入sex的值是否等于F/
if(tall>=150){
/判断tall是否大于等于150/
printf("A\n"); /当tall>=150时输出A/
}
else{
/当tall小于150时输出B/
printf("B\n");
}
}
else{
/判断sex不等于F执行/
if(tall>=170){
/判断tall值是否>=170/
printf("A\n"); /当tall>=170时输出A/
}
else{
printf("B\n"); /当tall小于170时输出B/
}
}
return 0;
}
if else matching principle
else is the closest to it at the same level, and there is no if statement matching with other else statements
switch (switch branch statement)
switch (expression) { case 1: statement group; break;
case 2:
statement group;
break;
case 3:
statement group;
break;
case n:
statement group;
break;
default;
statement group;
}
/*例子输入成绩查询等级*/
#include <stdio.h>
int main(){
int score;
int max;
printf("please input score");
scanf("%d",&score);
max = 0<score&&score<100 ? score/10:-1;
switch(max){
case 10:
printf("grade =A\n");
break;
case 9:
printf("grade =A\n");
break;
case 8:
printf("grade =B!\n");
break;
case 7:
printf("grade =C\n");
break;
case 6:
printf("grade =D/n");
break;
case 5:
case 4:
case 3:
case 2:
case 1:
case 0:
printf("sorry ! please study hard !/n");
break;
default:
printf("Input error again!/n" );
return 0;
}
} Conditional operator
example
if(a>b){ max=a; } else{ max=b } Let’s look at this example. When judging the values of a and b, is it a bit cumbersome to use branch statements, but we can use Conditional operators to simplify these things can be viewed as: a>b?a:b This means that when a>b is true, then a is the value of a>b, if it is false, then b is a> the value of b