例输入两个数并判断两数相等否 /*ch42.c*/ #include <stdio.h> main() int a,b; 运行： Enter integer a:12. printf("Enter integer a:"); Enter integer b:12. scanf("%d",&a); a-b printf("Enter integer b:") scanf("%d",&b); 运行： Enter integer a:12 if(a=-b) Enter integer b:9.J printf("a-bin"); a!=b else printf("a!=bin");
/*ch4_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"); } 例 输入两个数并判断两数相等否 运行：Enter integer a:12 Enter integer b:12 a==b 运行：Enter integer a:12 Enter integer b:9 a!=b
例判断输入字符种类 /*ch43.c*/ #include <stdio.h> mainO char c; printf("Enter a character:"); c-getcharO; if(c<0x20)printf("The character is a control character\n"); else if(c>0'&&c9)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&z)printf("The character is a lower lettern"); else printf("The character is other character n"); 运行：Enter a character:FlJ The character is other character
/*ch4_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"); } 例 判断输入字符种类 运行：Enter a character： The character is a control character 运行：Enter a character：8 The character is a digit 运行： Enter a character： D The character is a capital letter 运行： Enter a character： h The character is a lower letter 运行： Enter a character：F1 The character is other character
if语句嵌套： ●一般形式： if (expr1) if (expr1) if (expr2) if (expr2) 内嵌f statementl statementl 内嵌if else else statement3 statement2 if(expr1) if (expr1) statement1 else if(expr2)） statementI- else statement2 内嵌if if(expr3) else statement3 内嵌if if(expr3) statement3 else 内嵌if else statement4 statement4
vif语句嵌套： l一般形式： if (expr1) if (expr2) statement1 else statement2 else if(expr3) statement3 else statement4 内嵌if 内嵌if if (expr1) if (expr2) statement1 else statement2 内嵌if if (expr1) if (expr2) statement1 else statement3 内嵌if if (expr1) statement1 else if(expr3) statement3 else statement4 内嵌if
例输入两数并判断其大小关系 /*ch44.c*/ #include <stdio.h> main() int x,y; 运行：Enter integer x,y:12,23. printf("Enter integer x,y:") X<Y scanf("%d,%d",&x,&y); Enter integer x,y:12,6. X>Y ifxl与y) Enter integer x,y:12,12. if(x>y)printf("X>Yn"); X-Y else printf("X<Yn")方 else printf("X-Y\n");
例 输入两数并判断其大小关系 /*ch4_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"); } 运行：Enter integer x,y:12,23 X<Y Enter integer x,y:12,6 X>Y Enter integer x,y:12,12 X==Y
●if~else配对原则：缺省{}时，else总是和它 上面离它最近的未配对的f配对 rif.） Lelse. else. elSe
lif ~ else 配对原则：缺省{ }时，else总是和它 上面离它最近的未配对的if配对 if(.) if(.) if(.) else. else. else