Matrix operation

#include <bits/stdc++.h>
using namespace std;
#define ll long long

ll a[1009][1009],b[1009][1009],c[1009][1009];

int main()
{
    //as we declared the arrays globally so no need to set their value to 0 before applying multiplication
    ll n,m,i,j,p,q;
    char ax;
    printf("Welcome To Matrix Operations\n1.Type 'A/a' to perform addition\n2.Type 'S/s' to perform Subtraction\n3.Type 'M/m' to perform Multiplication\n");
    scanf("%c",&ax);
    if(ax=='A' || ax=='a')
    {
        printf("To perform Addition 2 Matrix Row and column must be same\nInputs for row and column\n");
        scanf("%lld %lld",&n,&m);
        puts("Inputs for First matrix");
        for(i=0; i<n; i++)
            for(j=0; j<m; j++)
                scanf("%lld",&a[i][j]);
        puts("Input for second matrix");
        for(i=0; i<n; i++)
            for(j=0; j<m; j++)
                scanf("%lld",&b[i][j]);
        for(i=0; i<n; i++)
            for(j=0; j<m; j++)
                c[i][j]=a[i][j]+b[i][j];
        printf("\nOutputs\n");
        for(i=0; i<n; i++)
        {
            for(j=0; j<m; j++)
                printf("%lld ",c[i][j]);
            printf("\n");
        }
    }
    else if(ax=='S' || ax=='s')
    {
        printf("To perform Subtraction 2 Matrix Row and column must be same\nInputs for Row and column\n");
        scanf("%lld %lld",&n,&m);
        puts("Inputs for First matrix");
        for(i=0; i<n; i++)
            for(j=0; j<m; j++)
                scanf("%lld",&a[i][j]);
        puts("Input for second matrix");
        for(i=0; i<n; i++)
            for(j=0; j<m; j++)
                scanf("%lld",&b[i][j]);
        for(i=0; i<n; i++)
            for(j=0; j<m; j++)
                c[i][j]=a[i][j]-b[i][j];
        printf("\nOutput\n");
        for(i=0; i<n; i++)
        {
            for(j=0; j<m; j++)
                printf("%lld ",c[i][j]);
            printf("\n");
        }
    }
    else if(ax=='M' || ax=='m')
    {
        printf("A's Row:    ");
        scanf("%lld",&n);
        printf("A's Column/B's Row:    ");
        scanf("%lld",&m);
        printf("B's Column:    ");
        scanf("%lld",&q);
        puts("Input for First matrix");
        for(i=0; i<n; i++)
            for(j=0; j<m; j++)
                scanf("%lld",&a[i][j]);
        puts("Input for Second matrix");
        for(i=0; i<m; i++)
            for(j=0; j<q; j++)
                scanf("%lld",&b[i][j]);
        for(i=0; i<n; i++)
            for(j=0; j<q; j++)
                for(p=0; p<m; p++)
                    c[i][j]+=a[i][p] * b[p][j];
        printf("\nOutput\n");
        for(i=0; i<n; i++)
        {
            for(j=0; j<q; j++)
            {
                printf("%lld ",c[i][j]);
            }
            printf("\n");
        }
    }
}