C语言英文课件4：选择结构.pptVIP

4.0 Foreword 【 ex. 4.1】Compute the cost of baggage carried by train.Input the weight of the baggage, compute the cost. standard of cost： (1) lighter then 50 kg(include 50 kg)， 0.35 yuan/kg (2) weighter then 50 kg，50 kg like (1)，the other excess, 0.50yuan/kg analysis： not overweight 0.35*weight cost overweight 0.35*50+0.5*(weight-50） 4.1 Algorithm and Description ?Algroithm：Some restricted steps are taked inorder to solve a special problem. ?features ：1. Limited(有穷性) 2. facticity(确定性)3. ≥0 input 4. 0 output 5. validity(有效性) ? describing algorithm：natural language,flow chart,pslanguage [example 4.1]algorithm description——natural language 1.input weight 2.comput value of pay based on weight 3.output value of pay details of step 2 ： if weight=50 则 pay=weight*0.35 else pay=50*0.35+(weight-50)*0.5 1.traditional flow chart(程序流程图) A figure describs steps of an algorithm with kinds of prescriptive graphic symbols and lines with arrowhead. symbols of flow chart： 【example 4.1】algorithm description—traditional flow chart 2. N-S structural flow chart Main feature：cancel flow line,adapt to structural programming, Can show the logical execute process of algorithm better basic shape of N-S flow chart： S1 block condition P while P is true T F S block S2 block S1 block S2 block S block until P is true (1)sequence (2)selective (3)while loop (4)until loop [example 4.1] algorithm description——N-S flow chart [ex. 4.1] Algorithm description—programming language Program list： main ( ) { float weight,pay; printf(?weight= ?); scanf(?%f ?, weight); if (weight=5