This is an interpreter for OriginalOldMan's esolang, A:;.

Acs.c

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

#define OP(op, code) case op: { code; } break
#define ERROR(fmt, v) return fprintf(stderr, fmt, v)
#define V(v) vars[strchr(vs, v) - vs]
#define F(v) strtod(V(v), NULL)

static int ic;
static char **insns, *vars[12];
static const char *vs = "jlbocqrtuvwx";

void print(char *s)
{
    char c;
    while ((c = *s++))
        s += putchar(c == '\\' ? '\n' : c) - c == '\\';
}

void run()
{
    size_t t, len;
    int d, ip = -1;
    char *p, *insn;

    while (++ip < ic) {
        insn = insns[ip];
        if ((p = strchr(vs, *insn)))
            vars[p - vs] = strdup(insn + 2);

        switch (*insn) {
            OP('p', print(V(insn[2])));
            OP('a', sprintf(V(insn[2]), "%.1f", F(insn[2]) + F(insn[4])));
            OP('s', sprintf(V(insn[2]), "%.1f", F(insn[2]) - F(insn[4])));
            OP('m', sprintf(V(insn[2]), "%.1f", F(insn[2]) * F(insn[4])));
            OP('d', sprintf(V(insn[2]), "%.1f", F(insn[2]) / F(insn[4])));
            OP('g', ip = atoi(insn + 2) - 1);
            OP('k', return);
            case 'i': case 'n':
                len = getline(&V(insn[2]), &t, stdin);
                V(insn[2])[--len] = '\0'; break;
            case '?':
            d = strcmp(V(insn[2]), V(insn[6]));
            if ((insn[4] == '=' && d) ||
                (insn[4] == '<' && d >= 0) ||
                (insn[4] == '>' && d <= 0))
                    ip += insn[8] - '0';
        }
    }
}

int main(int argc, char **argv)
{
    int c, i;
    FILE *src;

    if (argc != 2)
        ERROR("Usage: %s FILE\n", *argv);

    if (!(src = fopen(argv[1], "r")))
        ERROR("No such file: %s\n", argv[1]);

    for (i = 0; (c = fgetc(src)) != EOF; ++i) {
        if (strchr(";\n", c)) {
            fseek(src, -++i, SEEK_CUR);
            insns = realloc(insns, ++ic * sizeof insns);
            fread(insns[--ic] = malloc(i), i, 1, src);
            i = (insns[ic++][i - 1] = '\0') - 1;
        }
    }

    run();
    return 0;
}