Thread: Logic Gates - Multiplexer Help

Hi, I have to make a 2:1 multiplexer in C programming for an assignment

The user has to input A B & C (with C being the switcher)

Y is the output

Truth table

C	A	B	Y
0	0	0	0
0	0	1	0
0	1	0	1
0	1	1	1
1	0	0	0
1	0	1	1
1	1	0	0
1	1	1	1

**Updated the truth table, since I ..........ed up the first one



Like the image above but, S = C

We have to make it out of standard gates, (AND, OR, NOT etc)

I have done this so far, it has no errors (but doesn't return the correct numbers - BIG ERROR)

Code:

#include<stdio.h>int And1(int a, int b);
int And2(int b, int c);
int Not(int c);
int Or (int And1, int And2);


int main (void)
{
    int a;
    int b;
    int c;


printf("\nEnter Value for A: ");
scanf("%i", &a);


printf("\nEnter Value for B: ");
scanf("%i", &b);


printf("\nEnter Value for C: ");
scanf("%i", &c);




printf("\n\nValue from Multiplexer = %d", Or);
system("PAUSE"); 
return 0;
}
int Not(int c)
{
    int output;
if(c==0)
output=1;
else
output=0;
return (output);
}
int And1(int a, int Not)
{
int output;
 if(a==1 && Not==1)
  output=1;
else
  output=0;
 return (output);
}
int And2(int b, int c)
{
int output;
if (b==0 && c==0)
 output=0;
if (b==0 && c==1)
 output=0;
if(b==1 && c==0)
 output=0;
if(b==1 && c==1)
 output=1;
return (output);
}
int Or(int And1, int And2)
{
int output;
if(And1==0 && And2==0)
 output=0;
if(And1==1 && And2==0)
 output=1;
if(And1==0 && And2==1)
 output=1;
if(And1==1 && And2==1)
 output=1;
return (output);
}

Any help would be much appreciated, I have looked on numerous forums and can find nothing that matches this

Please indent your code properly.

I suggest that you simplify the implementation of your "logic gate" functions, e.g.,

Code:

int Or(int x, int y)
{
    return x || y;
}

It would make it so much easier to understand. Also, why are you naming your functions And1 and And2, then naming your parameters And1 and And2? It almost looks like you have a misunderstanding as to how to call functions.

Originally Posted by alexmallaburn

could you expand on this

You should indent your code to help denote blocks of scope. For example, instead of writing:

Code:

int Or(int And1, int And2)
{
int output;
if(And1==0 && And2==0)
output=0;
if(And1==1 && And2==0)
output=1;
if(And1==0 && And2==1)
output=1;
if(And1==1 && And2==1)
output=1;
return (output);
}

Write:

Code:

int Or(int And1, int And2)
{
    int output;
    if(And1==0 && And2==0)
        output=0;
    if(And1==1 && And2==0)
        output=1;
    if(And1==0 && And2==1)
        output=1;
    if(And1==1 && And2==1)
        output=1;
    return (output);
}

This way, it is easy to see what is the body of the function, and what are the bodies of the individual if statements. An indent level can consist of a number of spaces (I use 4, written by pressing tab) or a tab character.

Originally Posted by alexmallaburn

I'm unsure of how to call functions properly.

If we use the analogy of logic gates: when you define those functions, you are just "manufacturing" the logic gates (or designing a template thereof). To actually setup the circuit, you need to plugin the inputs and output and connect the gates together: this is like an actual function call that provides the functions with arguments and uses the return value of the function called.

Refer to anduril462's post #3 for examples.

Here is how I might write what you have now:

Code:

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

int And(int x, int y);
int Not(int x);
int Or(int x, int y);
int multiplexer(int x, int y, int z);

int main(void)
{
    int a;
    int b;
    int c;

    printf("\nEnter Value for A: ");
    scanf("%i", &a);

    printf("\nEnter Value for B: ");
    scanf("%i", &b);

    printf("\nEnter Value for C: ");
    scanf("%i", &c);

    printf("\n\nValue from Multiplexer = %d", multiplexer(a, b, c));

    system("PAUSE");
    return 0;
}

int Not(int x)
{
    return !x;
}

int And(int x, int y)
{
    return x && y;
}

int Or(int x, int x)
{
    return x || y;
}

Observe my indentation and how I do not have so many unnecessary blank lines.

I have taken the liberty of renaming your functions' parameters. You need to see clearly that naming a parameter And1 does not call the And1 function, and thus having And1 and And2 is redundant.

I have also taken the liberty of declaring a multiplexer function for you and calling it. How to implement it is up to you.

That is because of a typographical error. Fix it

Originally Posted by alexmallaburn

is it that there is two int x's

Exactly. Rename the second one to y.

Originally Posted by alexmallaburn

I have corrected that then i get a LNK2019 error

If you're attempting to build my example as-is, then that is to be expected: the multiplexer function has not been implemented.