C程序设计英文课件：CHAPTE 3 Control Flow.ppt

CHAPTE 3;Contents;3.1 Statements and Blocks;3.1 Statements and Blocks（语句与分程序）;3.1 Statements and Blocks;3.2 If-Else;3.2 If-Else;3.2 If-Else;3.2 If-Else;3.3 Else-If;3.3 Else-If;3.3 Else-If;3.3 Else-If;3.4 Switch;3.4 Switch;3.4 Switch;3.4 Switch;3.4 Switch;Example：count digit,white space, others main( ) { int c,i,nwhite,nother,ndigit[10]; nwhite=nother=0; for(i=0;i10;i++) ndigit[i]=0; while((c=getchar())!=EOF) { switch(c) { case ‘0’: case ‘1’: case ‘2’: case ‘3’: case ‘4’: case ‘5’: case ‘6’: case ‘7’: case ‘8’: case ‘9’: ndigit[c-’0’]++; break; case ‘ ’: case ‘\n’: case ‘\t’: nwhite++; break; default: nother++; break; } } …… };3.4 Switch;3.4 Switch;3.5 Loops-While and For;3.5 Loops-While and For;3.5 Loops-While and For;3.5 Loops-While and For;the expr1 and expr3 are omitted, equal to while for( ;i=100;) { sum+=i; i++; } all are omitted for ( ; ;) ? while(1) the expr1 can initialize other expressions for( sum=0;i=100; i++ ) sum+=i;;the expr1 and expr3 may be a Comma expression; for(sum=0,i=1; i=100; i++) sum+=i; for(i=0,j=100 ; ij; i++,j--) k=i+j; the expr2 is relational expression, 0 or not 0 for ( ; (c=getchar())!=‘\n’ ;) ;Example:convert s to integer #include ctype.h int atoi(char s[]) { int i,n,sign; for(i=0;isspace(s[i]);i++) ; sign=(s[i]==‘-’)? –1:1; if(s[i]==‘+’ || s[i]==‘-’) i++; for(n=0;isdigit(s[i]);i++) n=10*n+(s[i]-’0’); return sign*n; };Example: sort an array into increasing order void popsort(int v[ ],int n) /*起泡法*/ { int i,j,t; for(j=0;jn-1;j++) { for(i=0;in-1-j;i++) { if(v[i]v[i+1]) { t=v[i]; v[i]=v[i+1]; v[i+1]=t; } } } };Example:reverse string s in place #include string.h void reverse(char s[]) { int c,i,j; for(i=0, j=strlen(s)-1; ij; i++, j--) { c=s[ j ]; s[ j ]=s[