A general protection exception failure

This is a discussion on A general protection exception failure within the C Programming forums, part of the General Programming Boards category; Hi, I am programming something to change from infix to postfix notation, However I get a general protection exception when ...

  1. #1
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    Unhappy A general protection exception failure

    Hi, I am programming something to change from infix to postfix notation, However I get a general protection exception when i try to call the function that checs if the notation is correct.
    I don┤t even know what a general protection exception is, can someone tell me please what is it, and also, can someone help me to get rid of it, i┤ll place the first part of the code:


    Code:
    void cambio(int,int);    //esta funcion cambia entre las bases
    char *pedir_infija();    //esta funcion pide la expresion de forma infija
    char *posfija(char*);   //esta funcion cambia la expresion a postfija
    int comprobar(char*);   //comprueba que la expresión se haya dado de manera correcta
    int eval(char *);        //Da el resultado de la postfija
    int convnum(char);       //Convierte el caracter a su numero equivalente
    
    void main(){
    	clrscr();
    	int comp=0,resul=0,op=0,z=1,yapos=0,yain=0,sicon=0,base=10;
    	char *expre, *postex;
    	while(op!=4){
    		op=0;
    		while(op>z||op<1){
    			z=1;
    			printf("\n\n---------Convertidor de expresiones---------\n");
    			printf("\n%d. Aceptar infija",z++);
    			if(yain==1){
    				printf("\n%d. Convertir a postfija",z++);
    			}
    			if (yapos==1){
    				if(resul==-60){
    					printf("\nOperacion invalida division entre cero");
    				}else{
    					printf("\n%d. Evaluar postfija",z++);
    				}
    			}
    			printf("\n%d. Salir\n\n Opcion: ",z);
    			scanf("%d",&op);
    			getchar();
    		}
    		if(op==z)op=4;
    		switch(op){
    			case 1:
    				comp=0;
    				while(comp==0){   //mientras no sea valida la expresion la pedirI am silly de nuevo
    					printf("\nDame la expresion infija: ");
    					scanf("%s",&expre);
    					getchar();
    					comp=comprobar(expre);      /* general protectio exception is here*/
    				}
    				//printf("\nLa expresión infija es: %s",expre);
    				yain=1;
    				yapos=0;
    				break;
    			case 2:
    				postex=posfija(expre);   //llamada a la conversion a postfija
    				printf("Postfija: ");
    				printf("%s",postex);
    				resul=eval(postex);
    				yapos=1;
    				break;
    			case 3:
    				//calcula el resultado
    				printf("Resultado: %d",resul);
    				sicon=0;
    				while(sicon!=2){
    					sicon=0;
    					while(sicon>2||sicon<1){
    						printf("\nConvertir? (1.Si,2.No): ");
    						scanf("%d",&sicon);
    						getchar();
    					}
    					if(sicon!=2){
    						printf("\nEscribe la base: ");
    						scanf("%d",&base);
    						cambio(resul,base);
    					}
    				}
    				break;
    		}
    	}
    }
    
    
    
    
    
    int comprobar(char *expre){      /*here is where the function begins*/
    
    
    	int x,y=1,abr=0,cer=0;
    	for(x=0;x<strlen(expre);x++){   //va comprobando cada caracter
    		//comprueba de la lista de posibles caracteres que no haya ninguno
    		if(expre[x]!='+'&&expre[x]!='-'&&expre[x]!='*'&&expre[x]!='/'&&expre[x]!='%'&&expre[x]!='('&&expre[x]!=')'&&!isdigit(expre[x])) y=0;
    		if(expre[x]=='+'||expre[x]=='-'||expre[x]=='%'||expre[x]=='/'||expre[x]=='*'){     //En caso de que sea operador
    			if((!isdigit(expre[x-1])&&expre[x-1]!=')')||x==0){      //si el anterior a l operador no es un digito
    				y=0;
    			}
    		}
    		if(expre[x]=='('){     //cuenta parentesis abiertos
    			abr++;
    		}
    		if(expre[x]==')'){     //cuenta parentesis cerrados
    			cer++;
    		}
    		if(expre[x]==')'){     //verifica que cuando cierre parentesis lo anterior sea digito
    			if(!isdigit(expre[x-1])&&expre[x-1]!=')') y=0;
    		}
    	}
    	if(abr!=cer) y=0;  //si no son la misma cantidad de parentesis abiertos que cerrados
    	if(!isdigit(expre[strlen(expre)-1])&&expre[strlen(expre)-1]!=')') y=0;   //si el ultimo caracter es invalido
    	if(y==0) printf("Expresion Invalida\n\n");
    	return y;
    }
    
    }

    I wont┤paste the rest of the code, since it is very long as you can see

    thank you

  2. #2
    #include<xErath.h> xErath's Avatar
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    Use a debuger and see what happens step by step. The fault will happen somewhere in your code and you'll see where.

  3. #3
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    I have added in the code the place where it marks the mistake the step by step debugging process,
    Code:
    comp=comprobar(expre);      /* general protection exception is here*/
    However i can't figure out what the mistake is.

    I have also marked the function it is calling.

  4. #4
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    help please!

    I am really mad about this mistake

  5. #5
    #include<xErath.h> xErath's Avatar
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    Please post code that compiles, and post ALL the functions, otherwise there's no way to us to find tou what's wrong. Don't repost your code, edit the 1st post.

  6. #6
    Yes, my avatar is stolen anonytmouse's Avatar
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    Bad:
    Code:
    	char *expre;
    	scanf("%s",&expre);
    Better:
    Code:
    	char expre[100];
    	scanf("%.99s", expre);
    Unreadable:
    Code:
    if(expre[x] != '+' &&expre[x]!='-'&&expre[x]!='*'&&expre[x]!='/'&&expre[x]!='%'&&expre[x]!='('&&expre[x]!=')'&&!isdigit(expre[x])) y=0;
    Readable:
    Code:
    if (!strchr("+-*/%()", expre[x]) && !isdigit(expre[x]))
    {
    	y = 0;
    }
    Code:
    if((!isdigit(expre[x-1])&&expre[x-1]!=')')||x==0){
    What happens if x is 0?


    --
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    Last edited by anonytmouse; 11-24-2004 at 10:22 PM.

  7. #7
    ---
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    [edit]
    nvm
    my bad
    (i cant find my reading glasses )

  8. #8
    and the hat of wrongness Salem's Avatar
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    > void main(){
    > clrscr();
    Wow - void main, and the need to attempt to use a C++ compiler to compile this C code.

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