Correct output only when debugging

Question

I am having some trouble with a homework assignment in C. I have encountered an odd problem where the program gives me the expected output when running it with the debugger, but when running normally I get an odd result.

The program takes 2 polynomials and prints the sum and product of the 2. The input of a polynomial is simply in the form of [coefficient] [power] [coefficient] [power] and so on..

The sum is printed correctly. Here are the function used:

void printPolynome(MONOM* poly, int size)
 {
     int i;

     for (i=0; i<size; i++)
     {
         if ((poly[i].coefficient > 0)&&(i != 0))
             printf("+");

         if (poly[i].power == 0)
             printf("%d", poly[i].coefficient);
         else if (poly[i].power == 1)
         {
             printf("%dx", poly[i].coefficient);
         }
         else
            printf("%dx^%d", poly[i].coefficient, poly[i].power);
     }

     if (size == 0)
         printf("0");
 }

void printSumPolynomes(MONOM *p1, int s1, MONOM *p2, int s2)
 {
     int phSize = s1+s2;
     MONOM* res = (MONOM*) malloc(phSize * sizeof(MONOM)); // Worst case size of result polynome

     int i=0;
     int j=0;
     int resInd=0;
     int finalSize = 0;

     while ( (i<s1) && (j<s2) )
     {
         if (p1[i].power > p2[j].power)
         {
             res[resInd] = p1[i];
             i++;
         }
         else if (p1[i].power < p2[j].power)
         {
             res[resInd] = p2[j];
             j++;
         }
         // If numbers have the same power, sum the coefficients.
         else if (p1[i].power == p2[j].power)
         {
             if (p1[i].coefficient + p2[j].coefficient != 0)
             {
                 p1[i].coefficient += p2[j].coefficient;
                 res[resInd] = p1[i];
                 j++;
                 i++;
             }
             else
             {
                 j++;
                 i++;
                 resInd--;
                 finalSize--;
             }
         }

         resInd++;
         finalSize++;
     }
     // Take care of leftovers and add them to array.
     while (i < s1)
     {
         res[resInd] = p1[i];
         resInd++;
         i++;
         finalSize++;
     }
     while (j < s2)
     {
         res[resInd] = p2[j];
         resInd++;
         j++;
         finalSize++;
     }

     // Clip array if needed.
     if (phSize > finalSize)
        res = (MONOM*) realloc(res, finalSize * sizeof(MONOM));

     printPolynome(res, finalSize);
     free(res);
 }

void printMulPolynomes(MONOM *p1, int s1, MONOM *p2, int s2)
{
    int phSize = s1*s2;
    int i;
    int j;
    int resInd = 0;
    int mulSize = 0;

    MONOM* res = (MONOM*) malloc (phSize * sizeof(MONOM));

    for (i=0; i<s1; i++)
    {
        for (j=0; j<s2; j++)
        {
            res[resInd].coefficient = p1[i].coefficient * p2[j].coefficient;
            res[resInd].power = p1[i].power + p2[j].power;
            mulSize++;
            resInd++;
        }
    }

    // use sortInput function to sort the result.
    sortInput(res,mulSize);

    // calculate number of monoms in result
    i=0;
    mulSize = 0;
    while (res[i].power >= 0)
    {
        mulSize++;
        i++;
    }

    if (phSize > mulSize)
        res = (MONOM*) realloc(res, mulSize * sizeof(MONOM));

    printPolynome(res, mulSize);
    free(res);
}

Here is the getPolynome function:

MONOM* getPolynome(int* logSize)
 {
    int phSize = INIT_SIZE; // physical size
    int initLogSize = 0; // logical size of initial input
    int ch;
    int i = 0;
    int j = 0;
    int countLegalMonoms = 0;
    int countNums = 0;
    char* marker;
    char* userInput;
    char* token;
    MONOM* poly;
    BOOL sumFlag;
    int currCoef, currPow; // Variables for current coefficient and power input

    // Get the first char of input
    ch = getchar();

    // Create array for raw user input
    userInput = (char*) malloc (phSize * sizeof(char));

    while (ch != EOL)
    {
        if (phSize == initLogSize)
        {
            phSize *= 2;
            userInput = (char*) realloc (userInput, phSize);

        }

        userInput[i] = ch;
        initLogSize++;
        i++;

        // get next input
        ch = getchar();
    }
    userInput[i] = EOS;

    // Check how many numbers are in the array.
    marker = userInput;
    while (*marker != EOS)
    {
        if ( (*marker == ' ') || (*marker != ' ')&&(*(marker+1) == '\0') )
            countNums++;

        marker++;
    }

    // Create monoms array - a polynome
    poly = (MONOM*) malloc (countNums/2 * sizeof(MONOM));

    // Take the first token
    token = strtok(userInput, " ");

    while (token != NULL)
    {
        sumFlag = FALSE;

        sscanf(token, "%d", &currCoef);
        token = strtok(NULL, " ");
        sscanf(token, "%d", &currPow);

        // Check if the current power exists.
        for (i=0; i < countNums/2; i++)
        {
            if (poly[i].power == currPow)
            {
                poly[i].coefficient += currCoef;
                sumFlag = TRUE;

                // Check if the coeeficient sums to 0
                if (poly[i].coefficient == 0)
                    poly[i].power = COEF_NULL_FLAG; // Will be used later to remove from array.
            }
        }

        // Summation was not performed. Creating a new monom.
        if (sumFlag == FALSE)
        {
            poly[j].power = currPow;
            poly[j].coefficient = currCoef;
            j++;
        }

        token = strtok(NULL, " ");
    }


    // We now want to sort the array.
    sortInput(poly, j);

    // Count how many legal monoms are currently in the array
    for (i=0; i < j; i++)
    {
        if (poly[i].power != COEF_NULL_FLAG)
            countLegalMonoms++;
    }

    // Finished dealing with data - clip the array
    poly = (MONOM*) realloc (poly, countLegalMonoms * sizeof(MONOM));

    *logSize = countLegalMonoms;
    return poly;
}

This is the main function:

#define _CRT_SECURE_NO_WARNINGS
#define INIT_SIZE 2
#define EOL '\n'
#define EOS '\0'
#define COEF_NULL_FLAG -1
#define TRUE 1
#define FALSE 0

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct monom{ 
    int coefficient; 
    int power; 
}MONOM;

typedef int BOOL;

...

void main() {
    int myLogSize1, myLogSize2;
    MONOM* myPoly1;
    MONOM* myPoly2;

    printf("Please enter first polynome:");
    myPoly1 = getPolynome(&myLogSize1);
    printf("Please enter second polynome:");
    myPoly2 = getPolynome(&myLogSize2);

    printf("\n");
    printf("The sum of polynomes is: ");
    printSumPolynomes(myPoly1, myLogSize1, myPoly2, myLogSize2);
    printf("\n");
    printf("The multiplication of polynomes is: ");
    printMulPolynomes(myPoly1, myLogSize1, myPoly2, myLogSize2);

    printf("\n");


    free(myPoly1);
    free(myPoly2);
}

And here is the output I get for the following input:

Please enter first polynome:-2 2 2 3
Please enter second polynome:2 2

The sum of polynomes is: 2x^3
The multiplication of polynomes is: 4x^5-4x^4-33686019x^50865+5198872x^5177540+1
389377768x^201377471+5340200x^5349952+1428628924x^274+24x^2
Press any key to continue . . .

Thanks a lot for your help, I really cant find the source for all the extra garbage in my output.

phSize == initLogSize...userInput[i] = EOS; : It is not considered when allocating memory. — BLUEPIXY
– BLUEPIXY, Commented Jul 25, 2014 at 11:55

Optokopper · Accepted Answer · 2014-07-25 15:28:00Z

i assume the problem is in void printSumPolynomes(MONOM *p1, int s1, MONOM *p2, int s2):

// calculate number of monoms in result
i=0;
mulSize = 0;
while (res[i].power >= 0)
{
    mulSize++;
    i++;
}

this will only stop if you encounter a power less zero. As you didnt initialize you array res and only did

MONOM* res = (MONOM*) malloc (phSize * sizeof(MONOM));

it will scan through unallocated memory and causing garbage output.

AIUI you dont even need that code as you have your final size already in mulSize

EDIT: Actually mulSize is s1*s2, while this is the final size of your polynom, you could consider combining terms with corresponding powers, like it is done in getPolynome()

EDIT: Not explicitly initializing the res array is not causing the problem here, since all entries (2) will in fact be set with correct values, but the loop calculating the number of monoms does not terminate at the end of the array.

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