Calculator code wont work at all despite compiler showing 0 warnings

Question

I was doing some amateur C practice. As you can see I'm trying to make a slightly more advanced calculator that allows the user to decide what they want to do. Even though I clearly defined what to write in if() function, it wont work at all. I would type in "add" or "mul" in the console but it always returns, "type a given mathematical function" which is an outcome that I put in there to tell the user that they've given the wrong input. So far I've tried adding and removing the quotation mark in if() and replaced == with =. None of these work.

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

int main()
{
    int num1;
    int num2;
    int mfunc;

    printf("type in a mathematical function: add, subtract, divide or multiply ");
    scanf_s("%d", &mfunc);

    if (mfunc == "add") {
        printf("enter first number: ");
        scanf_s("%d", &num1);
        printf("enter a second number: ");
        scanf_s("%d", &num2);
        printf("sum of two number is: %d", num1 + num2);
    }
    else if (mfunc == "sub") {
        printf("enter first number: ");
        scanf_s("%d", &num1);
        printf("enter a second number: ");
        scanf_s("%d", &num2);
        printf("difference is: %d", num1 - num2);
    }
    else if (mfunc == "div") {
        printf("enter first number: ");
        scanf_s("%d", &num1);
        printf("enter a second number: ");
        scanf_s("%d", &num2);
        printf("quotent is: %d\n", num1 / num2);
    }
    else if (mfunc == "mul") {
        printf("enter first number: ");
        scanf_s("%d", &num1);
        printf("enter a second number: ");
        scanf_s("%d", &num2);
        printf("product is: %d", num1 * num2);
    }
    else {
        printf("type a given mathematical function");
    }

    return 0;
}

Answer 1

you can't compare "add" with myfunc. add is a string (array of chars of size 4), myfunc is an int. In C you can't compare int to string. you can compare string to string so you can ask from the user to input his func by write "add", but it is a bit more complex for you right now (you need to scan it to a proper array of chars and compare the strings using function which might be case sensitive, etc.). also, you can use instruction for the user - some kind of map so the user could insert 0 for add, 1 for sub and so on..

also, I used "define" witch is macro (an pre-processor directive) to more readable code;

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

#define ADD 0
#define SUB 1
#define DIV 3
#define MUL 4


int main()
{
int num1;
int num2;
int mfunc;

printf("type in a mathematical function: add, subtract, divide or multiply \n");
printf("to add insert 0,\nto subtract insert 1,\n");
printf("to divide insert 2,\nto multiply insert 3\n");
scanf("%d", &mfunc);

if (mfunc == ADD) {
    printf("enter first number: ");
    scanf("%d", &num1);
    printf("enter a second number: ");
    scanf("%d", &num2);
    printf("sum of two number is: %d", num1 + num2);
}
else if (mfunc == SUB) {
    printf("enter first number: ");
    scanf("%d", &num1);
    printf("enter a second number: ");
    scanf("%d", &num2);
    printf("difference is: %d", num1 - num2);
}
else if (mfunc == DIV) {
    printf("enter first number: ");
    scanf("%d", &num1);
    printf("enter a second number: ");
    scanf("%d", &num2);
    printf("quotent is: %d\n", num1 / num2);
}
else if (mfunc == MUL) {
    printf("enter first number: ");
    scanf("%d", &num1);
    printf("enter a second number: ");
    scanf("%d", &num2);
    printf("product is: %d", num1 * num2);
}
else {
    printf("type a given mathematical function");
}

return 0;
}

if you really want the user to input string you should be do that:

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



int main()
{
int num1;
int num2;
char mfunc[256];

printf("type in a mathematical function: add, subtract, divide or multiply \n");

gets(mfunc);

if (strcmp(mfunc, "ADD") == 0||strcmp(mfunc, "add") == 0) {
    printf("enter first number: ");
    scanf("%d", &num1);
    printf("enter a second number: ");
    scanf("%d", &num2);
    printf("sum of two number is: %d", num1 + num2);
}
else if (strcmp(mfunc, "SUB") == 0||strcmp(mfunc, "sub") == 0) {
    printf("enter first number: ");
    scanf("%d", &num1);
    printf("enter a second number: ");
    scanf("%d", &num2);
    printf("difference is: %d", num1 - num2);
}
else if ((strcmp(mfunc, "DIV") == 0||strcmp(mfunc, "div") == 0)) {
    printf("enter first number: ");
    scanf("%d", &num1);
    printf("enter a second number: ");
    scanf("%d", &num2);
    printf("quotent is: %d\n", num1 / num2);
}
else if ((strcmp(mfunc, "MUL") == 0||strcmp(mfunc, "mul") == 0)) {
    printf("enter first number: ");
    scanf("%d", &num1);
    printf("enter a second number: ");
    scanf("%d", &num2);
    printf("product is: %d", num1 * num2);
}
else {
    printf("type a given mathematical function");
}

return 0;
}

I know I used gets(), see paul-kapustin in this Q. How to read a line from the console in C?