(盐城工学院数据结构课程设计)栈的应用表达式求值(5)

栈的应用：表达式求值的设计

}

/******返回运算符号的优先级******/ int OperatorValue(char ValueToGive) {

if (ValueToGive == '(') return 6;

if (ValueToGive == ')') return 5;

if (ValueToGive == '^') return 3; if (ValueToGive == '%') return 2;

if (ValueToGive == '*') return 2;

if (ValueToGive == '/') return 2;

if (ValueToGive == '+') return 1;

if (ValueToGive == '-')

return 1; return 0; }

/******计算后缀表达式******/

void Calculate(FILE *Change, Stack Whereat, FILE *Temp) {

FStack Operands; float looker; char Op;

char spacefinder; float answer = 0; float NumA; float NumB;

Operands = (Ptr_Fn)malloc(sizeof(struct FNode)); Operands->Next= NULL;

while ((IsEmpty(Whereat) != 1) && PrintError != 1)

{ /*循环直到Whereat空，或者遇到错误*/

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栈的应用：表达式求值的设计

if (Top(Whereat) == 'A'){ fscanf(Temp,\ fscanf(Temp,\ /*如果是A,则是操作数*/ FPush(looker,Operands); Pop(Whereat); }

else if (Top(Whereat) == 'B'){ fscanf(Temp,\ /*如果是B,则是运算符*/ Op = getc(Temp); switch(Op){ /* 判断是什么运算符*/

case('^'): /*幂运算*/ NumB = FTop(Operands); FPop(Operands); if (FIsEmpty(Operands)){ /*错误处理*/ PrintError = 1; } else{ NumA = FTop(Operands); FPop(Operands);

if ((NumA == 0 && NumB < 0)||((NumA<0) && (NumB - (int)NumB != 0))) { PrintError = 1; } else{ answer = pow(NumA,NumB); FPush(answer,Operands); }

} break;

case '%': /*取模运算*/ NumB = FTop(Operands); FPop(Operands); if (FIsEmpty(Operands)){ /*错误处理*/ PrintError = 1; } else{ NumA = FTop(Operands);

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栈的应用：表达式求值的设计

FPop(Operands);

if ((NumA - (int)NumA != 0) || (NumB - (int)NumB != 0) || (NumB == 0)) { PrintError = 1; } else{ answer = (int)NumA % (int)NumB; FPush(answer,Operands); }

} break;

case '*': NumB = FTop(Operands); FPop(Operands); if (FIsEmpty(Operands)){ PrintError = 1; } else{ NumA = FTop(Operands); FPop(Operands); answer = NumA * NumB; FPush(answer,Operands); } break;

case '/': NumB = FTop(Operands); FPop(Operands); if (FIsEmpty(Operands)){ PrintError = 1; } else{ NumA = FTop(Operands); FPop(Operands); if (NumB == 0){ PrintError = 1; }

else{

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/* x mod b*/ /*乘法运算*/ /* x * y*/ /*除法运算*/ /*分母不为0*/

栈的应用：表达式求值的设计

answer = (float)(NumA / NumB); /* x / y*/ FPush(answer,Operands); } } break;

case '+': /*加法运算*/ NumB = FTop(Operands); FPop(Operands); if (FIsEmpty(Operands)){ PrintError = 1; } else{ NumA = FTop(Operands); FPop(Operands); answer = NumA + NumB; FPush(answer,Operands); } break;

case '-': NumB = FTop(Operands); FPop(Operands);

if (FIsEmpty(Operands)){ PrintError = 1; } else{ NumA = FTop(Operands); FPop(Operands);

answer = NumA - NumB;

FPush(answer,Operands);

} break; default: PrintError = 1; break; } Pop(Whereat); }

} 22

/* x + y*/ /*减法运算*/ /* x - y*/

/*判断结束*/ /*循环结束*/

栈的应用：表达式求值的设计

}

if (!PrintError){ answer = FTop(Operands); FPop(Operands); if (FIsEmpty(Operands) != 1){ fprintf(Change,\ /*如果还有操作数*/ PrintError = 0; } else fprintf(Change,\ }

else{ fprintf(Change,\ PrintError = 0; }

FMakeEmpty(Operands); free(Operands);

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