Spec:
Create a program that reads from a file and converts strings to integers (using a struct). Then add and subtract them.
Question/Problem:
I'm working on the adding function. I noticed that for numbers that add up and exceed the struct integer array (ie. sum->digits is an array in a struct). For example 55 + 55 = 110 (3 digits in a 2 digit array). So, what I'm trying to do is use Realloc() operator/function to extend the array in a struct by one more digit to store the carry over from the addition. The program fails when it runs the Realloc().
Code:/* * Peter Nguyen * COP 3502C - 0001 * Program 1 - BigIntegers * 01/27/10 */ #include <stdio.h> #include <stdlib.h> #include <string.h> struct integer { int* digits; int size; }; struct integer* convert_integer(char* stringInt); void print(struct integer *p); struct integer* add(struct integer *p, struct integer *q); struct integer* subtract(struct integer *p, struct integer *q); int compare(struct integer *p, struct integer *q); int main (void) { int numOflines; // Number of lines in "bigint.txt" file int i = 0, j = 0; int operator = 0; char string[201]; // Store string struct integer *num1, *num2, *answer; // Open "bigint.txt" file FILE * myFile; myFile = fopen("bigint.txt", "r"); // Reads number of operations fscanf(myFile, "%d", &numOflines); // Run loop for the number of operations for(i = 0; i < numOflines; i++) { // Read operator (1 = addition and 2 = subtraction) fscanf(myFile, "%d", &operator); // Read line and store the two strings fscanf(myFile, "%s", &string); num1 = convert_integer(string); fscanf(myFile, "%s", &string); num2 = convert_integer(string); print(num1); print(num2); if(operator == 1) { answer = add(num1, num2); print(answer); } // subtract function not written yet /* else if (operator == 2) answer = subtract(num1, num2); else // If operator is not + or - printf("The wrong operator!"\n); */ free(num1->digits); free(num1); free(num2->digits); free(num2); free(answer->digits); free(answer); } return 0; system("pause"); } ///////////////////////////////////////////////////////////////////// //Preconditions: the first parameter is string that stores // // only contains digits, doesn't start with // // 0, and is 200 or fewer characters long. // //Postconditions: The function will read the digits of the // // large integer character by character, // // convert them into integers and return a // // pointer to the appropriate struct integer. // ///////////////////////////////////////////////////////////////////// struct integer* convert_integer(char* stringInt) { int i, j = 0; struct integer *p = (struct integer*)(malloc(sizeof(struct integer))); // Allocate memory p->size = strlen(stringInt); p->digits = (int *)(malloc(sizeof(int)*p->size)); // Reverse the order for(i = p->size - 1; i >= 0; i--, j++) p->digits[i] = (int)(stringInt[j] - '0'); return p; } ///////////////////////////////////////////////////////////////////// //Preconditions: p is a pointer to a big integer. // //Postconditions: The big integer pointed to by p is // // printed out. // ///////////////////////////////////////////////////////////////////// void print(struct integer *p) { int i; for(i = p->size - 1; i >= 0; i--) printf("%d", p->digits[i]); printf("\n"); } ///////////////////////////////////////////////////////////////////// //Preconditions: p and q are pointers to struct integers. // //Postconditions: A new struct integer is created that // // stores the sum of the integers pointed to // // by p and q and a pointer to it is // // returned. // ///////////////////////////////////////////////////////////////////// struct integer* add(struct integer *p, struct integer *q) { struct integer *sum = (struct integer*)(malloc(sizeof(struct integer))); int i, num1, num2, carry = 0; sum->digits = (int*)(malloc(sizeof(int)*sum->size)); if(p->size > q->size) sum->size = p->size; else sum->size = q->size; for(i = 0; i <= sum->size; i++) { if(p->digits[i] == '\0') num1 = 0; else { num1 = p->digits[i]; if(q->digits[i] == '\0') num2 = 0; else num2 = p->digits[i]; if(i == sum->size && carry == 1) { sum->digits = (int*)realloc(sum->digits, (sum->size*sizeof(int))); num1 = 0; num2 = 0; } sum->digits[i] = num1 + num2 + carry; if(sum->digits[i] >= 10) { sum->digits[i] -= 10; carry = 1; } else carry = 0; } return sum; } ///////////////////////////////////////////////////////////////////// //Preconditions: p and q are pointers to struct integers. // //Postconditions: A new struct integer is created that // // stores the absolute value of the // // difference between the two and a pointer // // to this is returned. // ///////////////////////////////////////////////////////////////////// struct integer* subtract(struct integer *p, struct integer *q) { return 0; } ///////////////////////////////////////////////////////////////////// //Preconditions: Both parameters of the function are // // pointers to struct integer. // //Postconditions: The function compares the digits of two // // numbers and returns: // // -1 if the first number is smaller than the second, // // 0 if the first number is equal to the second number, // // 1 if the first number is greater than the second. // ///////////////////////////////////////////////////////////////////// int compare(struct integer *p, struct integer *q) { return 0; }
Originally Posted by Adak
. Thanks for the other tips.
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