The C Programming Language Chapter 5 Control Flow
The C Programming Language Chapter 5 Control Flow
Overview of C Statements
Selected Construction
if
switch
Loops
goto and if
while and do while
for
break and continue
The C Programming Language Chapter 5 Control Flow
5.1 Overview of C Statements
C statements,using a semicolon ; as a
statement
terminator ;
Kinds of C statements:
Expression statements:an expression flowed by,;”
Control statements (9 if( )~else~ switch
for( )~
while( )~
do~while( )
continue
break
goto
return
branches
loops
others
As total=total+limit ;
a=3 ;
func( ) ;
printf(“Hello,world!\n”) ;
Compound statements:using braces {…} to group
declarations and statements,so that they are
syntactically equivalent to a single statement.
o There is no,;” after the right brace.
As {
int x=1,y=2,z ;
z=x+y ;
printf(“%d”,z) ;
}
The C Programming Language Chapter 5 Control Flow
5.2 Selected Construction (if and switch)
if statement,has three syntax
if (expression) statement
flowchart
expr
statement
!0
=0
as if (x>y) printf(“%d”,x);
expr
statement1 statement2
!0 =0? if (expression)statement1
else
statement2
flowchart asif (x>y) max=x ;else max=y ;
The C Programming Language Chapter 5 Control Flow
if ( expr1 ) statement1
else if (expr2 ) statement2
else if (expr3 ) statement3
…...
[ else statement n ]
expr1
statemnt1
0
=0
expr2
expr3
statemntnstatemnt3statemnt2
0
0
=0
=0
flowchart
as if (salary>1000) index=0.4;
else if (salary>800) index=0.3;
else if (salary>600) index=0.2;
else if (salary>400) index=0.1;
else index=0;
The C Programming Language Chapter 5 Control Flow
as if (a==b&&x==y) printf(“a=b,x=y”);
if (3) printf(“OK”);
if (?a?) printf(“%d”,?a?);
if (x)? if (x!=0)
if(!x)? if(x==0)
as,
#include <stdio.h>
main()
{ int x,y;
scanf(“%d,%d”,&x,&y);
if(x>y)
x=y; y=x;
else
x++; y++;
printf(“%d,%d\n”,x,y);
}
Compile Error!
the value may be any type
may be compound statement
The C Programming Language Chapter 5 Control Flow
/*ch5_1.c*/
#include <stdio.h>
main()
{ int x,y;
printf("Enter an integer:");
scanf("%d",&x);
y=x;
if(y<0)
y= -y;
printf("\ninteger:%d--->absolute value:%d\n",x,y);
}
Enter an integer,-12?
integer:-12--->absolute value,12
The C Programming Language Chapter 5 Control Flow
/*ch5_2.c*/
#include <stdio.h>
main()
{ int a,b;
printf("Enter integer a:");
scanf("%d",&a);
printf(“Enter integer b:");
scanf("%d",&b);
if (a= =b)
printf(“a= =b\n");
else
printf(“a!=b\n");
}
Enter integer a:12?
Enter integer b:12?
a= =b
Enter integer a:12?
Enter integer b:9?
a!=b
The C Programming Language Chapter 5 Control Flow
/*ch5_3.c*/
#include <stdio.h>
main()
{ char c;
printf("Enter a character:");
c=getchar();
if(c<0x20) printf("The character is a control character\n");
else if(c>='0'&&c<='9') printf("The character is a digit\n");
else if(c>='A'&&c<='Z') printf("The character is a capital letter\n");
else if(c>='a'&&c<='z') printf("The character is a lower letter\n");
else printf("The character is other character\n");
}
Enter a character?
The character is a control character
t t 8?
t i digi
Enter a character D?
The character is a capital letter
Enter a character h
he c aracter is a lower let er
Enter a ch racter&?
The c ara te is other haracter
The C Programming Language Chapter 5 Control Flow
if statement can be nested
if (expr1)
if (expr2) statement1
else statement2
else
if (expr3) statement3
else statement4
nested if
nested if
if (expr1)
if (expr2)
statement1
else
statement2
nested if
if (expr1)
if (expr2)
statement1
else
statement2
nested if
if (expr1)
statement1
else
if(expr2)
statement2
else
statement3
nested if
The C Programming Language Chapter 5 Control Flow
/*ch5_4.c*/
#include <stdio.h>
main()
{ int x,y;
printf("Enter integer x,y:");
scanf("%d,%d",&x,&y);
if(x!=y)
if(x>y) printf("X>Y\n");
else printf("X<Y\n");
else
printf("X==Y\n");
}
Enter integer x,y:12,23?
X<Y
Enter integer x,y:12,6?
X>Y
Enter integer x,y:12,12?
X==Y
The C Programming Language Chapter 5 Control Flow
if-else association
associates the else with the closest previous
else-less if
if(……)
if(……)
if(……)
else…...else…...
else…...
as if (a= =b)
if (b= =c)
printf(“a= =b= =c”);
else
printf(“a!=b”);
Uses braces { } to force the proper association
main()
{ int x=100,a=10,b=20;
int v1=5,v2=0;
if (a<b)
if (b!=15)
if (!v1) x=1;
els
if(v2) x=10;
x=-1;
printf(“x=%d”,x);
} x=-1
The C Programming Language Chapter 5 Control Flow
flowchart
Switch statement? switch ( expr )
{ case E1,statement 1; break ;
case E2,statement 2; break;
…….
case En,statement n; break;
[default,statement ;break;]
}
…
as ……
case?A?:
case?B?:
case?C?,
printf(“score>60\n”);
break;
……..
switch
expression
statement1 statement2 statement n statement…...
E 1 E 2 En default
case
The C Programming Language Chapter 5 Control Flow
as,switch(score)
{ case 5,printf(“Very good!”);
case 4,printf(“Good!”);
case 3,printf(“Pass!”);
case 2,printf(“Fail!”);
default,printf(“data error!”);
}
when score is 5:
Very good! Good! Pass! Fail! data error!
The C Programming Language Chapter 5 Control Flow
main()
{ int x=1,y=0,a=0,b=0;
switch(x)
{ case 1:
switch(y)
{ case 0,a++; break;
case 1,b++; break;
}
case 2,a++;b++; break;
case 3,a++;b++;
}
printf(“\na=%d,b=%d”,a,b);
}
a=2,b=1
The C Programming Language Chapter 5 Control Flow
5.3 Loops
The goto Statement
The while Statement
The do ~ while Statement
The for Statement
The C Programming Language Chapter 5 Control Flow
goto label
….…..
labelstatements
goto
The C Programming Language Chapter 5 Control Flow
if and goto can make loops
/*ch5_1.c*/
#include <stdio.h>
main()
{ int i,sum=0;
i=1;
loop,if(i<=100)
{ sum+=i;
i++;
goto loop;
}
printf("%d",sum);
}
sum=0+1=1
sum=1+2=3
sum=3+3=6
sum=6+4=10
……
sum=4950+100=5050
terminationincrement
condition
loop body
initialization
The C Programming Language Chapter 5 Control Flow
while
while (expression)
satement
expr
statement
F(0)
T(!0)
while
The value of the expression is false
The C Programming Language Chapter 5 Control Flow
while
/*ch5_2.c*/
#include <stdio.h>
main()
{ int i,sum=0;
i=1;
while(i<=100)
{ sum=sum+i;
i++;
}
printf("%d",sum);
}
initialization
terminationincrement
condition
loop body
The C Programming Language Chapter 5 Control Flow
1~10
/*ch5_21.c*/
#include <stdio.h>
main()
{ int i=1;
while (i<=10)
{ printf("%d*%d=%d\n",i,i,i*i);
i++;
}
}
result
1*1=1
2*2=4
3*3=9
4*4=16
5*5=25
6*6=36
7*7=49
8*8=64
9*9=81
10*10=100
The C Programming Language Chapter 5 Control Flow
do
satement
while (expression)
flowchart
do
statement
expr
F(0)
T(!0) while
The statement is executed,then the
expression is evaluated;
Specifications
The body is always executed at least once
do~while => while
expr
statement
F(0)
T(!0)
statement
While
do~while
The C Programming Language Chapter 5 Control Flow
/*ch5_3.c*/
#include <stdio.h>
main()
{ int i,sum=0;
i=1;
do
{ sum+=i;
i++;
}while(i<=100);
printf("%d",sum);
}
do~while
The C Programming Language Chapter 5 Control Flow
compare while with do~while
/*ch5_4.c*/
#include <stdio.h>
main()
{ int i,sum=0;
scanf(“i=%d",&i);
do
{ sum+=i;
i++;
}while(i<=10);
printf(“sum=%d",sum);
}
/*ch5_41.c*/
#include <stdio.h>
main()
{ int i,sum=0;
scanf(“i=%d",&i);
while(i<=10)
{ sum+=i;
i++;
}
printf(“sum=%d",sum);
}
i=1
sum=55
i=1
sum=55
1
Su =11
1
=0
The C Programming Language Chapter 5 Control Flow
for
for ([expr1] ;[ expr2] ;[ expr3])
statement
flowchart
expr2
statement
F(0)
T(!0)
for
expr1
expr3
The C Programming Language Chapter 5 Control Flow
for for( initializationloop condition increment )
{
statements
}
specifications:
expr1,expr2,expr3 may be any types;
Any of the three parts can be omitted,although the
semicolons ; must remain.
Infinite loop,for( ; ; )
for=>while expr1;while (expr2)
{
statements
expr3;
}
for
#include <stdio.h>
main()
{ int i,sum=0;
for(i=1; i<=100 ;i++ )
sum+=i;
printf("%d",sum);
}
The C Programming Language Chapter 5 Control Flow
as#include<stdio.h>
main( )
{ int i=0;
for(i=0;i<10;i++)
putchar(?a?+i);
}
result abcdefghij
as#include<stdio.h>
main( )
{ int i=0;
for(;i<10;i++)
putchar(?a?+i);
}
as#include<stdio.h>
main( )
{ int i=0;
for(;i<10;)
putchar(?a?+(i++));
}
as#include<stdio.h>
main( )
{ int i=0;
for(;i<10;putchar(?a?+i),i++)
}
The C Programming Language Chapter 5 Control Flow
main()
{ int i,j,k;
for(i=0,j=100;i<=j;i++,j--)
{ k=i+j;
printf("%d+%d=%d\n",i,j,k);
}
}
#include<stdio.h>
main()
{ char c;
for(;(c=getchar())!='\n';)
printf("%c ",c);
}
The C Programming Language Chapter 5 Control Flow
Loops can be nested
(1) while()
{ ……
while()
{ ……
}
…...
}
(2) do
{ ……
do
{ ……
}while( );
…...
}while( );
(3) for( ; ; )
{ ……
for( ; ; )
{ ……
}
…...
}
(4) while()
{ ……
do
{ ……
}while( );
…….
}
(5) for( ; ; )
{ ……
while()
{ ……
}
…...
}
(6) do
{ ……
for( ; ; )
{ ……
}
…...
}while( );
The C Programming Language Chapter 5 Control Flow
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
2 4 6 8 10 12 14 16 18
3 6 9 12 15 18 21 24 27
9 18 27 36 45 54 63 72 81
…………
…..
i
j
/*ch5_5.c*/
#include <stdio.h>
main()
{ int i,j;
for(i=1;i<10;i++)
printf("%4d",i);
printf("\n---------------------------------------\n");
for(i=1;i<10;i++)
for(j=1;j<10;j++)
printf( (j==9)?"%4d\n":"%4d",i*j);
}
The C Programming Language Chapter 5 Control Flow
i<10
printf
F(0)
T(!0)
i=1
j++
j=1
j<10
T(!0)
F(0)
i++
for(i=1;i<10;i++)
for(j=1;j<10;j++)
printf((j==9)?"%4d\n":"%4d",i*j);
outer loop
inner loop
The C Programming Language Chapter 5 Control Flow
5.4 Break and Continue
Break
The break statement provides an
immediate exit from loops (while,
do~while and for ) or switch,
expr
……
break;
……
F(0)
T(!0)
whiledo
……
break;
…...
expr
F(0)
T(!0) while
expr2
……
break;
…...
F(0)
T(!0)
for
expr1
expr3
switch
expr
statement1
break;
statement2
break;
statementn
break;
statement
break;
…...
const 1 const 2 const n default
case
The C Programming Language Chapter 5 Control Flow
:100
#define PI 3.14159
main()
{
int r;
float area;
for(r=1;r<=10;r++)
{ area=PI*r*r;
if(area>100)
break;
printf("r=%d,area=%.2f\n",r,area);
}
}
break
The C Programming Language Chapter 5 Control Flow
:,
#include <stdio.h>
main()
{
int i,j;
char c;
while(1)
{ c=getchar();
if(c>='a' && c<='z')
putchar(c-'a'+'A');
else
break;
}
}
break
The C Programming Language Chapter 5 Control Flow
Continue
Skips the statements flow the continue,and causes the
next iteration of the loop(for,while,or do~while) to begin;
Applies only to loops,not to switch.
expr
……
continue;
……
F(0)
T(!0)
while
T(!0)
do
……
continue;
…...
expr
F(0)
while
expr2
……
continue;
…...
F(0)
T(!0)
for
expr1
expr3
The C Programming Language Chapter 5 Control Flow
/*ch5_12.c*/
#include <stdio.h>
main()
{ int i,num=0,a;
float sum=0;
for(i=0;i<10;i++)
{ scanf("%d",&a);
if(a<=0) continue;
num++;
sum+=a;
}
printf("%d plus integer's sum,%6.0f\n",num,sum);
printf("Mean value:%6.2f\n",sum/num);
}