阅读下列说明，回答问题。
【说明】
逻辑覆盖法是设计白盒测试用例的主要方法之一，通过对程序逻辑结构的遍历实现程序的覆盖。针对以下由C语言编写的程序，按要求回答问题。
int XOR(char * filename,unsigned long key){ FILE * input = NULL , *output =NULL; //i char * outfilename = NULL; int len = strlen(filename); unsigned char buffer; if( (filename[len-2] == '.')&& (filename[len-1] == 'c') ) { //2,3 outfilename = new char[len+1]; //4 strcpy(outfilename, filename); outfilename[len-2] = '\0'; } else{ //5 outfilename = new char[len+5]; strcpy(outfilename, filename); strncat(outfilename,".c",2); } input =fopen(filename,"rb"); if( input == NULL) { //6 cout ＜＜ "Error opening file " ＜＜ filename ＜＜ endl; //7 delete [] outfilename; outfilename = NULL; return 1; } output =fopen(outfilename,"wb"); if( output == NULL ) { //8 cout ＜＜ "Error creating output file " ＜＜ outfilename ＜＜ endl; //9 delete [] outfilename; outfilename = NULL; return 1; } while( ! feof(input) ) { //10 if(fread(&buffer,sizeof(unsigned char),1,input) != 1 ) { //11 if( ! feof(input) ) { //12 delete [] outfilename; //13 outfilename = NULL; fclose(input); fclose(output); return 1; } } else{ //14 buffer ^= key; fwrite(&buffer,sizeof(unsigned char),1,output); } } fclose(input); //15 fclose(output); delete [] outfilename; return 0; }
请画出上述程序的控制流图，并计算其控制流图的环路复杂度VG.
正确答案及解析
正确答案
解析
环路复杂度V(G)=8。
本问题考查白盒测试用例设计方法：基本路径法。涉及的知识点包括：根据代码绘制控制流图、计算环路复杂度。控制流图是描述程序控制流的一种图示方式，它由节点和定向边构成。控制流图的节点代表一个基本块，定向边代表控制流的方向。其中要特别注意的是，如果判断中的条件表达式是复合条件，即条件表达式是由一个或多个逻辑运算符连接的逻辑表达式，则需要改变复合条件的判断为一系列之单个条件的嵌套的判断。本题程序中，if( (filename[len-2]=='.')&&(filename[len-1]=='c') )这条判断语句中的判定由两个条件组成，因此在画控制流图的时候需要拆开成两条判断语句。程序的环路复杂度等于控制流图中判定节点的个数加1，本题控制流图中判定节点个数为7，所以V(G)=8。
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