黄建的C语言PPT课件,C02选择结构.ppt

2,分支结构,分支结构,2,本章内容,if 语句,if 语句,if 语句,1,if 语句,2011.3.7程序运行结果是 int x = 12; if (x 15) printf(“%d“, x - 5); if (x 5) printf(“%d“, x + 5);,17,2,if 语句,2011.3.10运行结果是 int x = 1, y = 2, t = 0; if (x = y) t = x; x = y; y = t; printf(“%d,%d“, x, y);,2011.3.10运行结果是 int x = 1, y = 2, t = 0; if (x = y) t = x; x = y; y = t; printf(“%d,%d“, x, y);,2,0,3,if 语句,2008.9.20运行结果是 int a = 1, b = 5, c = 3; if (a b) a = b, b = c; c = a; printf(“%d%d%d“, a, b, c);,2008.9.20运行结果是 int a = 1, b = 5, c = 3; if (a b) a = b, b = c; c = a; printf(“%d%d%d“, a, b, c);,151,交换变量的值,a,t,b,int a = 3, b = 4, t;,t = a;,a = b;,b = t;,3,4,3,4,3,t = b; b = a; a = t;,或,三个数排序2-1,if (a b) t = a; a = b; b = t; ,if (a c) t = a; a = c; c = t; ,if (b c) t = b; b = c; c = t; ,5,3,1,5,3,1,三个数排序2-2,if (a b) t = a; a = b; b = t; ,if (b c) t = b; b = c; c = t; ,if (a b) t = a; a = b; b = t; ,5,3,1,5,3,1,if - else 语句,1,if - else 语句,2005.9.7程序运行结果是 int a = 1, b = 2, c = 3; if (c = a) printf(“%d“, c); else printf(“%d“, b);,1,2,if - else 语句,2012.3.20运行结果是 int a = 3; if (a- 3) printf(“%d“, a); else printf(“%d“, -a);,1, , ,if ( 表达式1 ) else,if - else 语句嵌套,if ( 表达式2 ) 语句1; else 语句2;,if ( 表达式3 ) 语句3; else 语句4;,1,if - else 语句嵌套,例程序运行后，b的值是 int a = 3, b = 0; if (a 0) if (a 8) b = 5; else b = 7;,例程序运行后，b的值是 int a = 3, b = 0; if (a 0) if (a 8) b = 5; else b = 7;,0,2,if - else 语句嵌套,2011.9.18运行后b的值是 int a = 1, b = 0; if (-a) b+; else if (a = 0) b += 2; else b += 3;,2011.9.18运行后b的值是 int a = 1, b = 0; if (-a) b+; else if (a = 0) b += 2; else b += 3;,2,3,if - else 语句嵌套,2010.9.182011.3.27程序运行后，b的值是 int a = 1, b = 0; if (!a) b+; else if (a = 0) if (a) b += 2; else b += 3;,0,i,黄建语录,else总是与它前面最靠近的尚未配对的if配对使用。,f,语,句,黄建语录,switch 语句,break 语句,switch ( 1.0 ) ,case 1.0: case a 0: case 2: case 2: case3: case 4 + 5: case 6.0 7.0: default:,switch 语句,值不能是小数,一定要加空格,值不能相同,不能出现变量,default是可选项,可以是常量表