Thread: How to read variablles from txt and make sum,minus,multiply, divide with them?

I need to read read from text file line by line and make four operations. Example:
If the Input.txt file is like this:
3+5
2-1
4*3
8/4
My program should read the veriables, do the operations then create a Output.txt file in same path and write the answers int it.

This is my code so far and I'm stuck, reading the veriables but I don't know how to do operations and write to output.txt:

Code:

#include <stdio.h>

int main(int argc, char* argv[])
{
int i;
FILE* fptr = fopen("input.txt", "r"); 


if(fptr == NULL){
printf("\n Unable to open : %s ");
return -1;
}

}
fclose(fptr);
return 0;
}

It depends how complicated your expressions are.

Given your examples, a simple

Code:

int n1, n2;
char op;
if ( sscanf(output,"%d%c%d",&n1,&op,&n2) == 3 ) {
  if ( op == '+' )
}

It was half an answer (aka a hint) to see how far you could then go by yourself.

Apparently, not that far.

Post your effort, not "I tried ... and it didn't work".

One problem with beginner exercises is that handling text input correctly is quite difficult, because in theory the input file can be anything.

However it seems that you are guaranteed digit operator digit with no whitespace. So it should be relatively easy to parse from first princples.
Start by using fgets() to read each line at a time. The print out the lines to give yourself confidence that you are opening and reading the
file correctly. Then try to break up each line into an integer, a character for the operator, and another integer. Again, print them out
to satify yourself that the program is working correctly. Then put in the code to do the operation. Finally add the code to print out the
results to the output file, and you are done.

Originally Posted by mkache21

My program is working now but only if I give the input just like example. If I change the order of lines(order of +,-,*,/ operations) or add more lines it does not work properly.

That's no good. It's also surprising. The whole point of input is that the program reads it, and modifies its behaviour accordingly.

Code:

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

char operation, values[2][10]; 

float calculateFormula() {
    float result = 0.0;
    float left = atof(values[0]);
    float right = atof(values[1]);
    if (operation == '+') result = left + right;
    if (operation == '-') result = left - right;
    if (operation == '*') result = left * right;
    if (operation == '/') result = left / right;
    values[0][0] = '\0'; values[1][0] = '\0';
    return result;
}

void equate(char *calculate) { 
    char *ops = "+/-*";
    int side = 0, count = 0, skip = 0;
    for (int i=0; i < strlen(calculate)+1; i++) {
        skip = 0;
        for (int j=0; j < strlen(ops); j++) {
            if (calculate[i] == ops[j]) {
                operation = ops[j]; skip = 1;
                side = 1; count = 0; break;
            }
        } 
        if (calculate[i] == '\n' || calculate[i] == '\0') {
            side = 0; skip = 1; count = 0; 
            printf("%0.2f\n", calculateFormula() );
        }
        if (!skip) values[side][count++] = calculate[i];
    }
}

int main(int args, char *argv[]) {

    equate(" 3+5 \n 2-1 \n 4*3 \n 8/4 ");
  
    return 0;
}