
C语言基础知识-程序流程结构
作者:尹正杰
版权声明:原创作品,谢绝转载!否则将追究法律责任。
一.概述
C语言支持最基本的三种程序运行结构:顺序结构,选择结构,循环结构。
顺序结构:程序按顺序执行,不发生跳转。
选择结构:依据是否满足条件,有选择的执行相应功能。
循环结构:依据条件是否满足,循环多次执行某段代码。
二.选择结构
1>.if语句
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat if_demo.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #include <stdio.h> int main(void)
{
int a = ;
int b = ;
if (a > b)
{
printf("a > b\n");
} return ;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o if_demo if_demo.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./if_demo
a > b
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
2>.if ... else语句
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat if_demo2.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #include <stdio.h> int main(void)
{
int a = ;
int b = ;
if (a > b)
{
printf("a > b\n");
}
else
{
printf("a < b\n");
} return ;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o if_demo2 if_demo2.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./if_demo2
a < b
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
3>.if ... else if ...else语句
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat if_demo3.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #include <stdio.h> int main(void)
{
int a = ;
int b = ;
if (a > b)
{
printf("a > b\n");
}
else if(a == b)
{
printf("a == b\n");
}
else
{
printf("a < b\n");
} return ;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o if_demo3 if_demo3.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./if_demo3
a == b
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
4>.三目运算符【其实其内部判断条件和if相似,语法结构简单明了】
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat if_demo4.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #include <stdio.h> int main(void)
{
int a = ;
int b = ;
int max; if (a > b)
{
max = a;
}
else
{
max = b;
}
printf("s1 = %d\n",max); a = ;
b = ;
max = (a > b ? a:b); //上面一大堆代码,我们仅仅用三目运算符一行简写。三目运算符格式为"表达式?选项1[表达式]:选项2",即如果表达式为真,选择选项1的结果,如果为假则选择新选项2。
printf("s2 = %d\n",max); return ;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o if_demo4 if_demo4.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./if_demo4
s1 =
s2 =
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
5>.switch语句【注意:if 条件语句执行效率差,switch条件语句执行效率相对较高,但是if可以判断一个区间,而switch则只能用来判断一个值】
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat switch_demo.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #include <stdio.h> int main(void)
{
char c;
c = getchar(); //注意该方法只会接收第一个字符哟~比如你输入的是100,它只会接收第一个字符“1” switch(c) //参数只能是整型变量
{
case '':
printf("OK\n");
break; //switch遇到break就中断了
case '':
printf("not OK\n");
break;
default: //如果上面的条件都不满足,那么执行default
printf("are u OK?\n");
} return ;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o switch_demo switch_demo.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./switch_demo OK
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./switch_demo not OK
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./switch_demo are u OK?
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./switch_demo are u OK?
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
三.循环结构
1>.while语句
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat while_demo.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h> int main(void)
{
int a = ;
while(a < )
{
printf("a = %d\n",a);
a++;
system("sleep 0.5");
}
printf("程序执行完毕~\n"); return EXIT_SUCCESS;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o while_demo while_demo.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./while_demo
a =
a =
a =
a =
a =
a =
a =
a =
a =
程序执行完毕~
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
2>.do ... while语句
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat narcissus.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h> int main(void)
{
int index = ;
do
{
int one = , ten=, hundred=; //将一个三位数分解个位,十位,百位 hundred = index / ; //百位 ten = index / % ; //十位 one = index % ; //个位 if (hundred * hundred * hundred + ten * ten * ten + one * one * one == index) //各个位数的立方和等于该数本身,那么它就是一个水仙花
{
printf("%d是水仙花数\n",index);
} index ++;
}while(index < ); return EXIT_SUCCESS;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o narcissus narcissus.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./narcissus
153是水仙花数
370是水仙花数
371是水仙花数
407是水仙花数
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
3>.for循环
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat for_demo.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h> int main(void)
{
int index = ;
int sum = ; for(index = ;index<=;index++) //计算0-100之间所有数字的是总和
{
sum += index;
} printf("sum = %d\n",sum); return EXIT_SUCCESS;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o for_demo for_demo.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./for_demo
sum =
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat for_demo2.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h> int main(void)
{
for(int i = ;i<;i++)
{
int one = , ten=, hundred=; //将一个三位数分解个位,十位,百位 hundred = i / ; //百位 ten = i / % ; //十位 one = i % ; //个位 if (hundred * hundred * hundred + ten * ten * ten + one * one * one == i) //各个位数的立方和等于该数本身,那么它就是一个水仙花
{
printf("%d是水仙花数\n",i);
}
}
return EXIT_SUCCESS;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o for_demo2 for_demo2.c -std=c99 #注意,在Linux系统我们编译for循环代码时需要指定"-std=c99",否则会报错"error: ‘for’ loop initial declarations are only allowed in C99 mode"
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./for_demo2
153是水仙花数
370是水仙花数
371是水仙花数
407是水仙花数
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
使用for循环打印三位数存在的水仙花数字
4>.嵌套循环(循环之间可以相互嵌套)
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat for_99.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h> int main(void)
{
int i,j; #我们提前声明了变量i和j,如果我们在这里不声明直接在for循环里面声明也是可以的,只不过在Linux操作系统编译时,我们需要指定std的库为c99,默认使用的是c90库。否则会报错"error: ‘for’ loop initial declarations are only allowed in C99 mode"
for(i = ; i <= ; i++)
{
for(j=; j<=i; j++)
{
printf("%d x %d = %d\t",i,j,i * j);
}
printf("\n");
}
return EXIT_SUCCESS;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o for_99 for_99.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./for_99
x =
x = x =
x = x = x =
x = x = x = x =
x = x = x = x = x =
x = x = x = x = x = x =
x = x = x = x = x = x = x =
x = x = x = x = x = x = x = x =
x = x = x = x = x = x = x = x = x =
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
5>.循环语句练习一(猜年龄)
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat guess_age.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #include <stdio.h>
#include <time.h> int main(void)
{
srand((unsigned int)time(NULL)); //加入随机数种子
int num = rand()% + ;
int value;
for(;;)
{
printf("猜猜看我年龄多大(请输入一个整数)>>>: ");
scanf("%d",&value);
if(value > num)
{
printf("我有那么老吗?\n");
}
else if(value < num)
{
printf("我看起来这么小吗?\n");
}
else
{
printf("太棒了,你猜对啦~\n");
break;
}
}
return ;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o guess_age guess_age.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./guess_age
猜猜看我年龄多大(请输入一个整数)>>>:
我看起来这么小吗?
猜猜看我年龄多大(请输入一个整数)>>>:
我有那么老吗?
猜猜看我年龄多大(请输入一个整数)>>>:
我有那么老吗?
猜猜看我年龄多大(请输入一个整数)>>>:
我看起来这么小吗?
猜猜看我年龄多大(请输入一个整数)>>>:
我有那么老吗?
猜猜看我年龄多大(请输入一个整数)>>>:
我看起来这么小吗?
猜猜看我年龄多大(请输入一个整数)>>>:
太棒了,你猜对啦~
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
6>.循环语句练习二(打印等腰三角形)
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat isosceles_triangle.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #include <stdio.h> int main(void)
{
int row;
printf("请输入要打印等腰三角形的行数:>>> ");
scanf("%d",&row);
for (int i = ;i <= row;i++)
{
for (int j =;j <= row - i;j++)
{
printf(" ");
} for (int k = ;k <= i * -;k++)
{
printf("*");
}
printf("\n");
}
return ;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o isosceles_triangle isosceles_triangle.c -std=c99
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./isosceles_triangle
请输入要打印等腰三角形的行数:>>>
*
***
*****
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./isosceles_triangle
请输入要打印等腰三角形的行数:>>>
*
***
*****
*******
*********
***********
*************
***************
*****************
*******************
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
四.跳转语句break和contiune语句
1>.break语句
在switch条件语句和循环语句中都可以使用break语句:
当它出现在switch条件语句时,作用是终止某个case并跳出switch结构。
当它出现在循环语句中,作用是跳出当前内循环语句,执行后面的代码。
当它出现嵌套循环语句中,跳出最近的内层循环语句,执行后面的代码。
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat do_while.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h> int main(void)
{
int a = ;
do
{
a++;
if (a == )
{
break;
}
}while(a); //需要注意的是,尽管没有上面的if条件判断语句,该循环并非死循环,只是执行的次数较多而已,因为a是一个有符号int类型的数字,而int类型是有上限的 printf("%d\n",a); return EXIT_SUCCESS;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o do_while do_while.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./do_while [root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat do_while.c
2>.continue语句
在循环语句中,如果希望立即终止本次循环,并执行下一次循环,此时就需要使用continue语句。
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat continue_demo.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h> int main(void)
{
int index = ;
while (index < )
{
index++;
if(index % == || index % == || index / == ) //过滤掉带7和7的倍数的数字
{
continue;
}
printf("数字:%d\n",index);
} return EXIT_SUCCESS;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o continue_demo continue_demo.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./continue_demo
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
数字:
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat continue_demo.c #过滤掉带7和7的倍数的数字
3>.goto语句(无条件跳转,尽量少用)
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# cat goto_demo.c
/*
@author :yinzhengjie
blog:http://www.cnblogs.com/yinzhengjie
EMAIL:y1053419035@qq.com
*/ #include <stdio.h> int main(void)
{
goto END; //无条件跳转到END的标识
printf("第一行字母:a\n"); END: //我们定义的END标识,需要注意的是,这里是冒号(":"),而非分号(“;”)哟~
printf("第二行字母:A\n"); return ;
}
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# gcc -o goto_demo goto_demo.c
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]# ./goto_demo
第二行字母:A
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#
[root@node101.yinzhengjie.org.cn /yinzhengjie/code/day002]#