2.2.6循环结构程序设计 - 循环结构程序设计2.2

Loops-----WhileandForwhile:while(expression)statementForfor(expr1;expr2;expr3)statementexpr1;while(expr2){ statement expr3;} for(;;){……}inifinteloop:processingthefirstnelementofanarrayfor(i=0;i<n;i++)…zeroexpression?non-zerostatementLoops-----WhileandForExample1: #include<ctype.h> /*atoi:conveystointeger;version2*/

int

atoi(chars[]) {int

i,n,sign;

for(i=0;isspace(s[i]);i++);/*skipwhitespace*/ sign=(s[i]==‘-’)?-1:1; if(s[i]==‘+’||s[i]==‘-’)/*skipsign*/ i++;

for(n=0;isdigit(s[i]);i++) n=10*n+(s[i]-‘0’); returnsign*n; } Loops-----WhileandForExample2:/*shellshort:sortv[0]…v[n-1]intoincreasingorder*/voidshellshort(int

v[],intn) { int

gap,i,j,temp;

for(gap=n/2;gap>0;gap/=2)

for(i=gap;i<n;i++) for(j=i-gap;j>=0&&v[j]>v[j+gap];j-=gap){ temp=v[j];

v[j]=v[j+gap];

v[j+jap]=temp; } } for(i=1;i<n;i--)

for(j=j-1;j>=0&&v[j]>v[j+1];j-=1){temp=v[j];

v[j]=v[j+1];v[j+1]=temp;}Loops-----WhileandForExample3:

#include<string.h> /*reverse:reversestringsinplace*/ voidreverse(chars[]) { intc,i,j; for(i=0,j=strlen(s)-1;i<j;i++,j--){ c=s[i]; s[i]=s[j]; s[j]=c; } }Loops---Do-whilesyntax:

do statement while(expression); Example:

/*itoa:convertntocharactersins*/ voiditoa(intn,chars[]) {inti,sign; if((sign=n)<0)/*recordsign*/ n=-n; i=0; do{ s[i++]=n%10+’0’;/*getnextdigit*/ }while((n/=10)>0);/*deleteit*/ if(sign<0)s[i++]=‘-’; s[i]=‘\0’;reverse(s); }

BreakandContinuebreak:exittheloop

/*trim:removetrailingblanks,tabs,newlines*/inttrim(chars[]){intn; for(n=strlen(s)-1;n>=0;n--) if(s[n]!=‘‘&&s[n]!=‘\t’&&s[n]!=‘\n’)break; s[n+1]=‘\0’; returnn;}continue:causethenextiterationtobeginfor(i=0;i<n;i++){ if(a[i]<0)/*skipnegativeelement*/ continue;…/*dopositiveelements*/}

GotoandLabelssyntax:gotolabel_namelabel_name:statementsExample1: for(…) for(…){ if(disaster) gotoerror; } … error:cleanupthemess GotoandLabelswithgoto:

for(i=0;i<n;i++)for(j=0;j<m;j++) if(a[i]==b[j]) gotofound;/*didn’tfindanycommonelement*/…found:/*gotone:a[i]==b[j]*/ …

withoutgoto:found=0;for(i=0;i<n&&!found;i++)for(j=0;j<m&&!found;j++) if(a[i]==b[j])